--- type: Analog Component title: "LT8609 — 42V, 3A Synchronous Step-Down Regulator with 2.5µA Quiescent Current" description: "42V, 3A Synchronous Step-Down Regulator with 2.5µA Quiescent Current" resource: "https://www.analog.com/en/products/lt8609.html" tags: ["datasheet", "okf-r12-batch1", "linear"] generated: { by: "agentforge/aa0b0641", at: "2026-09-29T20:23:52Z" } status: draft sources: - id: "datasheet" resource: "https://www.analog.com/media/en/technical-documentation/data-sheets/lt8609-8609a-8609b.pdf" title: "LT8609 data sheet" author: "team:analog-devices" tables: - file: "lt8609/tables/table-00-p1-data.csv" title: "Pulse-Skipping Mode / Burst Mode Operation / Switch Edge Speed" page: 1 - file: "lt8609/tables/table-02-p2-data.csv" title: "Order Information" page: 2 - file: "lt8609/tables/table-03-p4-spec.csv" title: "Electrical Characteristics" page: 4 - file: "lt8609/tables/table-04-p15-data.csv" title: "Table 1. SW Frequency vs RT Value" page: 15 - file: "lt8609/tables/table-05-p28-data.csv" title: "Revision History" page: 28 - file: "lt8609/tables/table-06-p30-data.csv" title: "Related Parts" page: 30 - file: "lt8609/tables/table-01-p2-abs_max.csv" title: "Absolute Maximum Ratings" page: 2 figures: - file: "lt8609/figures/lt8609-eqx01.png" caption: "Equation as printed (p. 1)" type: equation page: 1 - file: "lt8609/figures/lt8609-f000.png" caption: "" type: "application_circuit" page: 1 - file: "lt8609/figures/lt8609-f001.png" caption: "12VIN to 5VOUT Efficiency" type: "characteristic_curve" page: 1 - file: "lt8609/figures/lt8609-f002.png" caption: "" type: "pinout" page: 2 - file: "lt8609/figures/lt8609-f004.png" caption: "LT8609 Efficiency (3.3V Output, Burst Mode Operation) (8609 G01)" type: "characteristic_curve" page: 6 - file: "lt8609/figures/lt8609-f005.png" caption: "LT8609 Efficiency (5V Output, Burst Mode Operation) (8609 G04)" type: "characteristic_curve" page: 6 - file: "lt8609/figures/lt8609-f006.png" caption: "LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) (8609 G07)" type: "characteristic_curve" page: 6 - file: "lt8609/figures/lt8609-f007.png" caption: "LT8609 Efficiency (3.3V Output, Burst Mode Operation) (8609 G02)" type: "characteristic_curve" page: 6 - file: "lt8609/figures/lt8609-f008.png" caption: "LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) (8609 G05)" type: "characteristic_curve" page: 6 - file: "lt8609/figures/lt8609-f009.png" caption: "LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) (8609 G08)" type: "characteristic_curve" page: 6 - file: "lt8609/figures/lt8609-f010.png" caption: "LT8609 Efficiency (5V Output, Burst Mode Operation) (8609 G03)" type: "characteristic_curve" page: 6 - file: "lt8609/figures/lt8609-f011.png" caption: "LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) (8609 G06)" type: "characteristic_curve" page: 6 - file: "lt8609/figures/lt8609-f012.png" caption: "FB Voltage" type: "characteristic_curve" page: 6 - file: "lt8609/figures/lt8609-f013.png" caption: "LT8609A-3.3 VOUT Voltage" type: "characteristic_curve" page: 7 - file: "lt8609/figures/lt8609-f014.png" caption: "LT8609A-5 VOUT Voltage" type: "characteristic_curve" page: 7 - file: "lt8609/figures/lt8609-f015.png" caption: "Line Regulation" type: "characteristic_curve" page: 7 - file: "lt8609/figures/lt8609-f016.png" caption: "No-Load Supply Current Tested in Regulation" type: "characteristic_curve" page: 7 - file: "lt8609/figures/lt8609-f017.png" caption: "Top FET Current Limit vs Duty Cycle" type: "characteristic_curve" page: 7 - file: "lt8609/figures/lt8609-f018.png" caption: "Load Regulation" type: "characteristic_curve" page: 7 - file: "lt8609/figures/lt8609-f019.png" caption: "No-Load Supply Current vs Temperature (N ot Switching)" type: "characteristic_curve" page: 7 - file: "lt8609/figures/lt8609-f020.png" caption: "Top FET Current Limit vs Temperature" type: "characteristic_curve" page: 7 - file: "lt8609/figures/lt8609-f021.png" caption: "Switch Drop vs Temperature" type: "characteristic_curve" page: 8 - file: "lt8609/figures/lt8609-f022.png" caption: "Minimum On-Time vs Temperature" type: "characteristic_curve" page: 8 - file: "lt8609/figures/lt8609-f023.png" caption: "Dropout Voltage vs Load Current" type: "characteristic_curve" page: 8 - file: "lt8609/figures/lt8609-f024.png" caption: "Switch Drop vs Switch Current" type: "characteristic_curve" page: 8 - file: "lt8609/figures/lt8609-f025.png" caption: "Minimum Off-Time vs Temperature" type: "characteristic_curve" page: 8 - file: "lt8609/figures/lt8609-f026.png" caption: "Switching Frequency vs Temperature" type: "characteristic_curve" page: 8 - file: "lt8609/figures/lt8609-f027.png" caption: "Burst Frequency vs Load Current" type: "characteristic_curve" page: 9 - file: "lt8609/figures/lt8609-f028.png" caption: "Minimum Load to Full Frequency (SYNC Float to 1.9V)" type: "characteristic_curve" page: 9 - file: "lt8609/figures/lt8609-f029.png" caption: "Soft-Start Tracking" type: "characteristic_curve" page: 9 - file: "lt8609/figures/lt8609-f030.png" caption: "Soft-Start Current vs Temperature" type: "characteristic_curve" page: 9 - file: "lt8609/figures/lt8609-f031.png" caption: "Case Temperature vs Load Current" type: "characteristic_curve" page: 9 - file: "lt8609/figures/lt8609-f032.png" caption: "Frequency Foldback" type: "characteristic_curve" page: 9 - file: "lt8609/figures/lt8609-f033.png" caption: "VIN UVLO" type: "characteristic_curve" page: 9 - file: "lt8609/figures/lt8609-f034.png" caption: "Case Temperature vs 3A Pulsed Load" type: "characteristic_curve" page: 9 - file: "lt8609/figures/lt8609-f036.png" caption: "Switching Waveforms (8609 G33)" type: "characteristic_curve" page: 10 - file: "lt8609/figures/lt8609-f037.png" caption: "Switching Waveforms (8609 G34)" type: "characteristic_curve" page: 10 - file: "lt8609/figures/lt8609-f038.png" caption: "Transient Response (8609 G36)" type: "characteristic_curve" page: 10 - file: "lt8609/figures/lt8609-f039.png" caption: "Start-Up Dropout (8609 G38)" type: "characteristic_curve" page: 10 - file: "lt8609/figures/lt8609-f040.png" caption: "Switching Waveforms (8609 G35)" type: "characteristic_curve" page: 10 - file: "lt8609/figures/lt8609-f041.png" caption: "Transient Response (8609 G37)" type: "characteristic_curve" page: 10 - file: "lt8609/figures/lt8609-f042.png" caption: "Start-Up Dropout (8609 G39)" type: "characteristic_curve" page: 10 - file: "lt8609/figures/lt8609-f043.png" caption: "" type: "block_diagram" page: 12 - file: "lt8609/figures/lt8609-f044.png" caption: "" type: "unclassified_image" page: 14 - file: "lt8609/figures/lt8609-f045.png" caption: "Figure 1a. SW Burst Mode Frequency vs Load" type: "characteristic_curve" page: 14 - file: "lt8609/figures/lt8609-f046.png" caption: "Figure 2. Burst Mode Operation" type: "scope_capture" page: 14 - file: "lt8609/figures/lt8609-f047.png" caption: "Figure 3. Reverse V IN Protection" type: "application_circuit" page: 20 - file: "lt8609/figures/lt8609-f048.png" caption: "Figure 4. PCB Layout" type: "layout_drawing" page: 21 - file: "lt8609/figures/lt8609-f049.png" caption: "Figure 5. Case Temperature Rise vs Load Current" type: "characteristic_curve" page: 22 - file: "lt8609/figures/lt8609-f050.png" caption: "" type: "application_circuit" page: 22 - file: "lt8609/figures/lt8609-f051.png" caption: "" type: "characteristic_curve" page: 22 - file: "lt8609/figures/lt8609-f052.png" caption: "Figure 6. Case Temperature Rise vs 3A Pulsed Load" type: "application_circuit" page: 22 - file: "lt8609/figures/lt8609-f053.png" caption: "" type: "application_circuit" page: 23 - file: "lt8609/figures/lt8609-f054.png" caption: "" type: "application_circuit" page: 23 - file: "lt8609/figures/lt8609-f055.png" caption: "" type: "application_circuit" page: 23 - file: "lt8609/figures/lt8609-f056.png" caption: "" type: "application_circuit" page: 24 - file: "lt8609/figures/lt8609-f057.png" caption: "" type: "application_circuit" page: 24 - file: "lt8609/figures/lt8609-f058.png" caption: "MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I)" type: "other" page: 25 - file: "lt8609/figures/lt8609-f059.png" caption: "" type: "other" page: 26 - file: "lt8609/figures/lt8609-f060.png" caption: "" type: "other" page: 27 - file: "lt8609/figures/lt8609-f061.png" caption: "" type: "other" page: 27 - file: "lt8609/figures/lt8609-f062.png" caption: "" type: "other" page: 27 - file: "lt8609/figures/lt8609-f063.png" caption: "RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS" type: "other" page: 27 - file: "lt8609/figures/lt8609-f064.png" caption: "Tracking 3.3V and 1.8V 2MHz Converters" type: "application_circuit" page: 30 - file: "lt8609/figures/lt8609-eq01.png" caption: "Equation as printed (p. 15)" type: equation page: 15 - file: "lt8609/figures/lt8609-eq02.png" caption: "Equation as printed (p. 15)" type: equation page: 15 - file: "lt8609/figures/lt8609-eq03.png" caption: "Equation as printed (p. 16)" type: equation page: 16 - file: "lt8609/figures/lt8609-eq04.png" caption: "Equation as printed (p. 16)" type: equation page: 16 - file: "lt8609/figures/lt8609-eq05.png" caption: "Equation as printed (p. 16)" type: equation page: 16 - file: "lt8609/figures/lt8609-eq06.png" caption: "Equation as printed (p. 16)" type: equation page: 16 - file: "lt8609/figures/lt8609-eq07.png" caption: "Equation as printed (p. 16)" type: equation page: 16 - file: "lt8609/figures/lt8609-eq08.png" caption: "Equation as printed (p. 17)" type: equation page: 17 - file: "lt8609/figures/lt8609-eq09.png" caption: "Equation as printed (p. 18)" type: equation page: 18 agentforge: part_number: "LT8609" collection: "okf-r12-batch1" --- # LT8609 — 42V, 3A Synchronous Step-Down Regulator with 2.5µA Quiescent Current *Datasheet: [LT8609 data sheet (PDF)](https://www.analog.com/media/en/technical-documentation/data-sheets/lt8609-8609a-8609b.pdf)* ### FEATURES - Wide Input Voltage Range: 3.0V to 42V ![Equation as printed (p. 1)](lt8609/figures/lt8609-eqx01.png) - Ultralow Quiescent Current Burst Mode ® Operation: - <2.5µA I Q Regulating 12V IN to 3.3V OUT - Output Ripple <10mV P-P - High Efficiency 2MHz Synchronous Operation: - >93% Efficiency at 1A, 5V OUT from 12V IN - 3A Maximum Continuous Output - Fast Minimum Switch-On Time: 45ns - LT8609A Available in Fixed 3.3V and 5V Output - Adjustable and Synchronizable: 200kHz to 2.2MHz - Spread Spectrum Frequency Modulation for Low EMI - Allows Use of Small Inductors - Low Dropout - Peak Current Mode Operation - Accurate 1V Enable Pin Threshold - Internal Compensation - Output Soft-Start and T racking - Small 10-Lead MSOP Package, 16-Lead MSOP Package, or 10-Lead 3mm × 3mm DFN Package with Side Wettable Flanks - AEC-Q100 Qualified for Automotive Applications ### APPLICATIONS - GSM Transceivers - General Purpose Step-Down - Low EMI Step-Down All registered trademarks and trademarks are the property of their respective owners. ### DESCRIPTION The LT ® 8609/LT8609A/LT8609B is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 1.7µA of nonswitching quiescent current. The LT8609/LT8609A/ LT8609B can deliver 3A of continuous current. Burst Mode operation enables high efficiency down to very low output currents while keeping the output ripple below 10mV P-P . A SYNC pin allows synchronization to an external clock, or spread spectrum modulation for low EMI operation. Internal compensation with peak current mode topology allows the use of small inductors and results in fast transient response and good loop stability. The EN/UV pin has an accurate 1V threshold and can be used to program V IN UVLO or to shut down the part. A capacitor on the TR/SS pin programs the output voltage ramp rate during start-up while the PG flag signals when V OUT is within ±8.5% on the adjustable output parts or ±7.5% on the fixed output parts of the programmed output voltage as well as fault conditions. The LT8609A has slower switch edges for lower EMI emissions. The LT8609B operates in pulse-skipping mode only. **Pulse-Skipping Mode / Burst Mode Operation / Switch Edge Speed** ([table-00-p1-data.csv](lt8609/tables/table-00-p1-data.csv), p. 1) | | PULSE-SKIPPING MODE, Burst Mode OPERATION | SWITCH EDGE SPEED | |---|---|---| | LT8609 | Both | Fast | | LT8609A | Both | Medium | | LT8609B | Pulse-Skipping | Fast | ### 12VIN to 5V OUT Efficiency 8609 TA01b Rev. J ### TYPICAL APPLICATION ### 5V, 2MHz Step-Down ### ABSOLUTE MAXIMUM RATINGS (Note 1) VIN , EN/UV, PG — 42V FB, TR/SS — 4V SYNC, V OUT — 6V Operating Junction Temperature Range (Note 2) LT8609E/LT8609AE/LT8609BE — -40°C to 125°C LT8609I/LT8609AI/LT8609BI — -40°C to 125°C LT8609H/LT8609AH — -40°C to 150°C LT8609AJ — -40°C to 150°C Storage Temperature Range — -65°C to 150°C ### PIN CONFIGURATION ### ORDER INFORMATION **Order Information** ([table-02-p2-data.csv](lt8609/tables/table-02-p2-data.csv), p. 2) | LEAD FREE FINISH | TAPE AND REEL | PART MARKING* | PACKAGE DESCRIPTION | TEMPERATURE RANGE | |---|---|---|---|---| | LT8609EMSE#PBF | LT8609EMSE#TRPBF | LTGRW | 10-Lead Plastic MSOP | −40°C to 125°C | | LT8609IMSE#PBF | LT8609IMSE#TRPBF | LTGRW | 10-Lead Plastic MSOP | −40°C to 125°C | | LT8609HMSE#PBF | LT8609HMSE#TRPBF | LTGRW | 10-Lead Plastic MSOP | −40°C to 150°C | | LT8609AEMSE#PBF | LT8609AEMSE#TRPBF | LTGVR | 10-Lead Plastic MSOP | −40°C to 125°C | | LT8609AIMSE#PBF | LT8609AIMSE#TRPBF | LTGVR | 10-Lead Plastic MSOP | −40°C to 125°C | | LT8609AJMSE#PBF | LT8609AJMSE#TRPBF | LTGVR | 10-Lead Plastic MSOP | −40°C to 150°C | | LT8609AHMSE#PBF | LT8609AHMSE#TRPBF | LTGVR | 10-Lead Plastic MSOP | −40°C to 150°C | | LT8609BEMSE#PBF | LT8609BEMSE#TRPBF | LTGZY | 10-Lead Plastic MSOP | −40°C to 125°C | | LT8609BIMSE#PBF | LT8609BIMSE#TRPBF | LTGZY | 10-Lead Plastic MSOP | –40°C to 125°C | | LT8609AEMSE16#PBF | LT8609AEMSE16#TRPBF | 8609A | 16-Lead Plastic MSOP | –40°C to 125°C | | LT8609AIMSE16#PBF | LT8609AIMSE16#TRPBF | 8609A | 16-Lead Plastic MSOP | –40°C to 125°C | | LT8609AJMSE16#PBF | LT8609AJMSE16#TRPBF | 8609A | 16-Lead Plastic MSOP | –40°C to 150°C | | LT8609AHMSE16#PBF | LT8609AHMSE16#TRPBF | 8609A | 16-Lead Plastic MSOP | –40°C to 150°C | | LT8609AEDDM#PBF | LT8609AEDDM#TRPBF | LHJZ | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 125°C | | LT8609AJDDM#PBF | LT8609AJDDM#TRPBF | LHJZ | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | | LT8609AHDDM#PBF | LT8609AHDDM#TRPBF | LHJZ | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | | LT8609AEDDM-3.3#PBF | LT8609AEDDM-3.3#TRPBF | LHKB | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 125°C | | LT8609AJDDM-3.3#PBF | LT8609AJDDM-3.3#TRPBF | LHKB | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | | LT8609AEDDM-5#PBF | LT8609AEDDM-5#TRPBF | LHKC | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 125°C | | LT8609AJDDM-5#PBF | LT8609AJDDM-5#TRPBF | LHKC | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | | LT8609AHDDM-5#PBF | LT8609AHDDM-5#TRPBF | LHKC | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | | **AUTOMOTIVE PRODUCTS**** | | | | | | LT8609EMSE#WPBF | LT8609EMSE#WTRPBF | LTGRW | 10-Lead Plastic MSOP | –40°C to 125°C | | LT8609IMSE#WPBF | LT8609IMSE#WTRPBF | LTGRW | 10-Lead Plastic MSOP | –40°C to 125°C | | LT8609HMSE#WPBF | LT8609HMSE#WTRPBF | LTGRW | 10-Lead Plastic MSOP | –40°C to 150°C | | LT8609AEMSE#WPBF | LT8609AEMSE#WTRPBF | LTGVR | 10-Lead Plastic MSOP | –40°C to 125°C | | LT8609AIMSE#WPBF | LT8609AIMSE#WTRPBF | LTGVR | 10-Lead Plastic MSOP | –40°C to 125°C | | LT8609AJMSE#WPBF | LT8609AJMSE#WTRPBF | LTGVR | 10-Lead Plastic MSOP | –40°C to 150°C | | LT8609AHMSE#WPBF | LT8609AHMSE#WTRPBF | LTGVR | 10-Lead Plastic MSOP | –40°C to 150°C | | LT8609AEMSE16#WPBF | LT8609AEMSE16#WTRPBF | 8609A | 16-Lead Plastic MSOP | –40°C to 125°C | | LT8609AIMSE16#WPBF | LT8609AIMSE16#WTRPBF | 8609A | 16-Lead Plastic MSOP | –40°C to 125°C | | LT8609AJMSE16#WPBF | LT8609AJMSE16#WTRPBF | 8609A | 16-Lead Plastic MSOP | –40°C to 150°C | | LT8609AHMSE16#WPBF | LT8609AHMSE16#WTRPBF | 8609A | 16-Lead Plastic MSOP | –40°C to 150°C | | LT8609AEDDM#WPBF | LT8609AEDDM#WTRPBF | LHJZ | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 125°C | | LT8609AJDDM#WPBF | LT8609AJDDM#WTRPBF | LHJZ | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | | LT8609AHDDM#WPBF | LT8609AHDDM#WTRPBF | LHJZ | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | | LT8609AEDDM-3.3#WPBF | LT8609AEDDM-3.3#WTRPBF | LHKB | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 125°C | | LT8609AJDDM-3.3#WPBF | LT8609AJDDM-3.3#WTRPBF | LHKB | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | | LT8609AEDDM-5#WPBF | LT8609AEDDM-5#WTRPBF | LHKC | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 125°C | | LT8609AJDDM-5#WPBF | LT8609AJDDM-5#WTRPBF | LHKC | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | | LT8609AHDDM-5#WPBF | LT8609AHDDM-5#WTRPBF | LHKC | 10-Lead (3mm × 3mm) Plastic Side Wettable DFN | –40°C to 150°C | - **\*:** The temperature grade is identified by a label on the shipping container. - **\*\*:** Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for these models. Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container . Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. ### ELECTRICAL CHARACTERISTICS ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = 25°C. | PARAMETER | CONDITIONS | | MIN | TYP | MAX | UNITS | |----------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|-----|-------------------------|-------------------------|-------------------------|-------------| | Minimum Input Voltage | | l | | 2.7 | 3.0 3.2 | V | | V IN Quiescent Current | LT8609/LT8609A: V EN/UV = 0V, V SYNC = 0V V EN/UV = 2V, Not Switching, V SYNC = 0V | l | | 1 1.7 | 4 12 | µA µA | | V IN Current in Regulation | LT8609B: V EN/UV = 0V V EN/UV = 2V, Not Switching LT8609/LT8609A: V IN = 6V, V OUT = 2.7V, Output Load = 100µA V IN = 6V, V OUT = 2.7V, Output Load = 1mA | l l | 350 | 1 46 480 | 4 90 700 | µA µA µA µA | | | LT8609A-3.3: V IN = 8V, V OUT = 3.3V I LOAD = 100µA V IN = 8V, V OUT = 3.3V I LOAD = 1mA | l l | | 46 480 | 90 700 | µA µA | | | LT8609A-5: V IN = 12V, V OUT = 5V I LOAD = 100µA V IN = 12V, V OUT = 5V I LOAD = 1mA | l l | | 46 480 | 90 700 | µA µA | | Feedback Reference Voltage | LT8609/LT8609A: (E-, I-, H-Grade) V IN = 6V, I LOAD = 100mA V IN = 6V, I LOAD = 100mA | l | 0.778 0.770 | 0.782 0.782 | 0.786 0.794 | V V | | | LT8609/LT8609A: (J-Grade) V IN = 6V, I LOAD = 100mA V IN = 6V, I LOAD = 100mA LT8609B: V IN = 6V, I LOAD = 100mA V IN = 6V, I LOAD = 100mA | l l | 0.778 0.766 0.772 0.759 | 0.782 0.782 0.782 0.782 | 0.786 0.798 0.792 0.805 | V V V V | | Output Reference Voltage | LT8609A-3.3: V IN = 8V, I LOAD = 100mA V IN = 8V, I LOAD = 100mA | l | 3.291 3.25 | 3.3 3.3 | 3.309 3.35 | V V | | | LT8609A-5: V IN = 12V, I LOAD = 100mA V IN = 12V, I LOAD = 100mA | l | 4.97 4.89 | 5 5 | 5.03 5.11 | V V | | Feedback Voltage Line Regulation | LT8609/LT8609A: V IN = 4.0V to 40V | l | | 0.004 | 0.02 | %/V | | Feedback Voltage Line Regulation | LT8609B: V IN = 4.0V to 40V | l | | 0.004 | 0.04 | %/V | | Output Voltage Line Regulation | LT8609A-3.3: V IN = 4.0V to 40V | l | | 0.004 | 0.02 | %/V | | Output Voltage Line Regulation | LT8609A-5: V IN = 6.0V to 40V | l | | 0.004 | | %/V | | Feedback Pin Input Current | LT8609/LT8609A/LT8609B: V FB = 1.0V | l | | | 0.02 | | | Output Pin Input | LT8609A-3.3: | l | | | ±20 | nA | | Current | V OUT = 4.0V | | | 620 | | nA | | Output Pin Input Current | LT8609A-5: V OUT = 6.0V | l | | 425 | | nA | | Minimum On-Time | I LOAD = 1.5A, SYNC = 0V I LOAD = 1.5A, SYNC = 1.9V | l l | | 45 45 | 75 60 | ns ns | | Minimum Off Time | | | | 90 | 130 | ns | ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = 25°C. **Electrical Characteristics** ([table-03-p4-spec.csv](lt8609/tables/table-03-p4-spec.csv), p. 4) | PARAMETER | CONDITIONS | MIN | TYP | MAX | UNITS | OVERTEMP | |---|---|---|---|---|---|---| | Minimum Input Voltage | | | | 3.0 | V | | | Minimum Input Voltage | | | 2.7 | 3.2 | V | ● | | V_IN Quiescent Current | LT8609/LT8609A: V_EN/UV = 0V, V_SYNC = 0V | | 1 | 4 | µA | | | V_IN Quiescent Current | LT8609/LT8609A: V_EN/UV = 2V, Not Switching, V_SYNC = 0V | | 1.7 | 12 | µA | ● | | V_IN Quiescent Current | LT8609B: V_EN/UV = 0V | | 1 | 4 | µA | | | V_IN Quiescent Current | LT8609B: V_EN/UV = 2V, Not Switching | | 350 | | µA | | | V_IN Current in Regulation | LT8609/LT8609A: V_IN = 6V, V_OUT = 2.7V, Output Load = 100µA | | 46 | 90 | µA | ● | | V_IN Current in Regulation | LT8609/LT8609A: V_IN = 6V, V_OUT = 2.7V, Output Load = 1mA | | 480 | 700 | µA | ● | | V_IN Current in Regulation | LT8609A-3.3: V_IN = 8V, V_OUT = 3.3V I_LOAD = 100µA | | 46 | 90 | µA | ● | | V_IN Current in Regulation | LT8609A-3.3: V_IN = 8V, V_OUT = 3.3V I_LOAD = 1mA | | 480 | 700 | µA | ● | | V_IN Current in Regulation | LT8609A-5: V_IN = 12V, V_OUT = 5V I_LOAD = 100µA | | 46 | 90 | µA | ● | | V_IN Current in Regulation | LT8609A-5: V_IN = 12V, V_OUT = 5V I_LOAD = 1mA | | 480 | 700 | µA | ● | | Feedback Reference Voltage | LT8609/LT8609A: (E-, I-, H-Grade) V_IN = 6V, I_LOAD = 100mA | 0.778 | 0.782 | 0.786 | V | | | Feedback Reference Voltage | LT8609/LT8609A: (E-, I-, H-Grade) V_IN = 6V, I_LOAD = 100mA | 0.770 | 0.782 | 0.794 | V | ● | | Feedback Reference Voltage | LT8609/LT8609A: (J-Grade) V_IN = 6V, I_LOAD = 100mA | 0.778 | 0.782 | 0.786 | V | | | Feedback Reference Voltage | LT8609/LT8609A: (J-Grade) V_IN = 6V, I_LOAD = 100mA | 0.766 | 0.782 | 0.798 | V | ● | | Feedback Reference Voltage | LT8609B: V_IN = 6V, I_LOAD = 100mA | 0.772 | 0.782 | 0.792 | V | | | Feedback Reference Voltage | LT8609B: V_IN = 6V, I_LOAD = 100mA | 0.759 | 0.782 | 0.805 | V | ● | | Output Reference Voltage | LT8609A-3.3: V_IN = 8V, I_LOAD = 100mA | 3.291 | 3.3 | 3.309 | V | | | Output Reference Voltage | LT8609A-3.3: V_IN = 8V, I_LOAD = 100mA | 3.25 | 3.3 | 3.35 | V | ● | | Output Reference Voltage | LT8609A-5: V_IN = 12V, I_LOAD = 100mA | 4.97 | 5 | 5.03 | V | | | Output Reference Voltage | LT8609A-5: V_IN = 12V, I_LOAD = 100mA | 4.89 | 5 | 5.11 | V | ● | | Feedback Voltage Line Regulation | LT8609/LT8609A: V_IN = 4.0V to 40V | | 0.004 | 0.02 | %/V | ● | | Feedback Voltage Line Regulation | LT8609B: V_IN = 4.0V to 40V | | 0.004 | 0.04 | %/V | ● | | Output Voltage Line Regulation | LT8609A-3.3: V_IN = 4.0V to 40V | | 0.004 | 0.02 | %/V | ● | | Output Voltage Line Regulation | LT8609A-5: V_IN = 6.0V to 40V | | 0.004 | 0.02 | %/V | ● | | Feedback Pin Input Current | LT8609/LT8609A/LT8609B: V_FB = 1.0V | | | ±20 | nA | ● | | Output Pin Input Current | LT8609A-3.3: V_OUT = 4.0V | | 620 | | nA | ● | | Output Pin Input Current | LT8609A-5: V_OUT = 6.0V | | 425 | | nA | ● | | Minimum On-Time | I_LOAD = 1.5A, SYNC = 0V | | 45 | 75 | ns | ● | | Minimum On-Time | I_LOAD = 1.5A, SYNC = 1.9V | | 45 | 60 | ns | ● | | Minimum Off Time | | | 90 | 130 | ns | | | **Oscillator Frequency** | | | | | | | | Oscillator Frequency | LT8609/LT8609A: R_T = 221k, I_LOAD = 0.5A | 155 | 200 | 245 | kHz | ● | | Oscillator Frequency | LT8609/LT8609A: R_T = 60.4k, I_LOAD = 0.5A | 640 | 700 | 760 | kHz | ● | | Oscillator Frequency | LT8609/LT8609A: R_T = 18.2k, I_LOAD = 0.5A | 1.925 | 2.00 | 2.075 | MHz | ● | | Oscillator Frequency | LT8609B: R_T = 18.2k, I_LOAD = 0.5A | 1.875 | 2.00 | 2.125 | MHz | ● | | Top Power NMOS On-Resistance | I_LOAD = 1A | | 185 | | mΩ | | | Top Power NMOS Current Limit | | 3.4 | 4.5 | 5.7 | A | ● | | Bottom Power NMOS On-Resistance | | | 115 | | mΩ | | | SW Leakage Current | V_IN = 42V, V_SW = 40V | | | 15 | µA | ● | | EN/UV Pin Threshold | EN/UV Rising | 0.99 | 1.05 | 1.11 | V | ● | | EN/UV Pin Hysteresis | | | 50 | | mV | | | EN/UV Pin Current | LT8609/LT8609A: V_EN/UV = 2V | | | ±20 | nA | ● | | EN/UV Pin Current | LT8609B: V_EN/UV = 2V | | | ±30 | nA | ● | | PG Upper Threshold Offset from V_FB | LT8609/LT8609A: V_FB Rising | 5 | 8.5 | 13 | % | ● | | PG Upper Threshold Offset from V_FB | LT8609B: V_FB Rising | 4 | 8.5 | 14 | % | ● | | PG Upper Threshold Offset from V_OUT | LT8609A-3.3/LT8609A-5 V_OUT Rising | 5 | 7.5 | 11 | % | ● | | PG Lower Threshold Offset from V_FB | LT8609/LT8609A: V_FB Falling | 5 | 8.5 | 13 | % | ● | | PG Lower Threshold Offset from V_FB | LT8609B: V_FB Falling | 4 | 8.5 | 14 | % | ● | | PG Lower Threshold Offset from V_OUT | LT8609A-3.3/LT8609A-5 V_OUT Falling | 5 | 7.5 | 11 | % | ● | | PG Hysteresis | | | 0.5 | | % | | | PG Leakage | V_PG = 42V | | | ±200 | nA | ● | | PG Pull-Down Resistance | V_PG = 0.1V | | 550 | 1200 | Ω | | | Sync Low Input Voltage | LT8609/LT8609A | 0.4 | 0.9 | | V | ● | | Sync High Input Voltage | LT8609/LT8609A: INTV_CC = 3.5V | | 2.7 | 3.2 | V | ● | | TR/SS Source Current | | 1 | 2 | 3 | µA | ● | | TR/SS Pull-Down Resistance | Fault Condition, TR/SS = 0.1V | | 300 | 900 | Ω | | | Spread Spectrum Modulation Frequency | LT8609/LT8609A: V_SYNC = 3.3V | 1 | 3 | 6 | kHz | | *OVERTEMP: ● marks a limit specified over the full operating temperature range; a blank cell means the limit is specified at TA = 25°C only.* - **Note 1:** Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. - **Note 2:** The LT8609E/LT8609AE/LT8609BE is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the -40°C to 125°C operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. The LT8609I/LT8609AI/LT8609BI is guaranteed over the full -40°C to 125°C operating junction temperature range. The LT8609H/LT8609AH/LT8609AJ is guaranteed over the full -40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures greater than 125°C. - **Note 3:** This IC includes overtemperature protection that is intended to protect the device during overload conditions. Junction temperature will exceed 150°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature will reduce lifetime. ### TYPICAL PERFORMANCE CHARACTERISTICS LT8609 Efficiency (5V Output, Burst Mode Operation) LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) LT8609 Efficiency (3.3V Output, Burst Mode Operation) LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) LT8609 Efficiency (5V Output, Burst Mode Operation) LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) Line Regulation Line Regulation Top FET Current Limit vs Duty Cycle Top Fet Current Limit vs Duty Cycle CHANGE IN V OUT (%) Switch Drop vs Temperature Switch Drop vs Temperature Minimum On-Time vs Temperature Minimum On-Time Vs Temperature Minimum Off-Time vs Temperature Minimum Off-Time Vs Temperature Switching Frequency vs Temperature Switching Frequency Vs Temperature Soft-Start T racking Soft-Start T racking Soft-Start Current vs Temperature Soft Start Current Vs Temperature Case Temperature vs 3A Pulsed Load Case Temperature vs 3A Pulsed Load ### Switching Waveforms 12V IN TO 5V OUT AT 1A ### Transient Response 50mA TO 1A TRANSIENT 12V IN TO 5V OUT C OUT = 47µF ### Start-Up Dropout Start-Up Dropout ### Switching Waveforms ### Transient Response ### Start-Up Dropout Start-Up Droupout 36V IN TO 5V OUT AT 1A ### Switching Waveforms ### PIN FUNCTIONS BST: This pin is used to provide a drive voltage, higher than the input voltage, to the topside power switch. Place a 0.1µF boost capacitor as close as possible to the IC. Do not place a resistor in series with this pin. SW: The SW pin is the output of the internal power switches. Connect this pin to the inductor and boost capacitor . This node should be kept small on the PCB for good performance. INTV CC : Internal 3.5V Regulator Bypass Pin. The internal power drivers and control circuits are powered from this voltage. INTV CC max output current is 20mA. Voltage on INTV CC will vary between 2.8V and 3.5V. Decouple this pin to power ground with at least a 1µF low ESR ceramic capacitor . Do not load the INTV CC pin with external circuitry. RT: A resistor is tied between RT and ground to set the switching frequency. SYNC: External Clock Synchronization Input. Ground this pin for low ripple Burst Mode operation at low output loads. Tie to a clock source for synchronization to an external frequency. Leave floating for pulse-skipping mode with no spread spectrum modulation. Tie to INTV CC or tie to a voltage between 3.2V and 5.0V for pulse-skipping mode with spread spectrum modulation. When in pulse-skipping mode, the I Q will increase to several mA. In the LT8609B, the SYNC pin is replaced with a no connect; the LT8609B operates in pulse-skipping mode without spread spectrum. FB (LT8609/LT8609A/LT8609B ONLY): The LT8609/ LT8609A/LT8609B adjustable output parts regulate the FB pin to 0.782V. Connect the feedback resistor divider tap to this pin. VOUT (LT8609A-3.3/LT8609-5 ONLY): The LT 8609A-3.3 regulates to V OUT pin to 3.3V. This pin connects a 5.9MΩ internal feedback divider that programs the fixed output. The LT8609A-5 regulates to V OUT pin to 5V. This pin connects a 8.95MΩ internal feedback divider that programs the fixed output. TR/SS: Output T racking and Soft-Start Pin. This pin allows user control of output voltage ramp rate during start-up. A TR/SS voltage below 0.782V forces the LT8609/LT8609A/ LT8609B to regulate the FB pin to equal the TR/SS pin voltage. In the LT8609A-3.3 and LT8609A-5 fixed output voltage options the output voltage will track the TR/SS pin voltage based on a factor set by the internal feedback resistor divider . The 3.3V output options will track to a voltage 4.2 times that of the TR/SS pin, while the 5V output options will track to a voltage 6.39 times that of the TR/SS pin. When TR/SS is above 0.782V, the tracking function is disabled and the internal reference resumes control of the error amplifier . An internal 2µA pull-up current from INTV CC on this pin allows a capacitor to program output voltage slew rate. This pin is pulled to ground with a 300Ω MOSFET during shutdown and fault conditions; use a series resistor if driving from a low impedance output. PG: The PG pin is the open-drain output of an internal comparator. On the LT8609/LT8609A/LT8609B adjustable output parts, PG remains low until the FB pin is within ±8.5% of the final regulation voltage, and there are no fault conditions. On the LT8609A-3.3/LT8609A-5 fixed output parts, PG remains low until the V OUT pin is within ±7.5% of the final regulation voltage, and there are no fault conditions. PG is valid when V IN is above 3.2V, regardless of EN/UV pin state. VIN : The V IN pin supplies current to the LT8609/LT8609A/ LT8609B internal circuitry and to the internal topside power switch. This pin must be locally bypassed. Be sure to place the positive terminal of the input capacitor as close as possible to the V IN pins, and the negative capacitor terminal as close as possible to the GND pins. EN/UV: The LT8609/LT8609A/LT8609B is shut down when this pin is low and active when this pin is high. The hysteretic threshold voltage is 1.05V going up and 1.00V going down. Tie to V IN if the shutdown feature is not used. An external resistor divider from V IN can be used to program a V IN threshold below which the LT8609/LT8609A/ LT8609B will shut down. GND: Exposed Pad Pin. The exposed pad must be connected to the negative terminal of the input capacitor and soldered to the PCB in order to lower the thermal resistance. ### BLOCK DIAGRAM ### OPERATION The LT8609/LT8609A/LT8609B is a monolithic constant frequency current mode step-down DC/DC converter . An oscillator with frequency set using a resistor on the RT pin turns on the internal top power switch at the beginning of each clock cycle. Current in the inductor then increases until the top switch current comparator trips and turns off the top power switch. The peak inductor current at which the top switch turns off is controlled by the voltage on the internal VC node. The error amplifier servos the VC node by comparing the voltage on the V FB pin with an internal 0.782V reference. The LT8609A-5 and LT8609A-3.3 Fixed output parts use the V OUT pin and an internal resistor divider to generate an internal FB node. When the load current increases it causes a reduction in the feedback voltage relative to the reference leading the error amplifier to raise the VC voltage until the average inductor current matches the new load current. When the top power switch turns off the synchronous power switch turns on until the next clock cycle begins or inductor current falls to zero. If overload conditions result in excess current flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level. If the EN/UV pin is low, the LT8609/LT8609A/LT8609B is shut down and draws 1µA from the input. When the EN/UV pin is above 1V, the switching regulator becomes active. To optimize efficiency at light loads, the LT8609/LT8609A enters Burst Mode operation during light load situations. Between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current to 1.7µA. In a typical application, 2.5µA will be consumed from the input supply when regulating with no load. The SYNC pin is tied low to use Burst Mode operation and can be floated to use pulse-skipping mode. If a clock is applied to the SYNC pin the part will synchronize to an external clock frequency and operate in pulse-skipping mode. While in pulse-skipping mode the oscillator operates continuously and positive SW transitions are aligned to the clock. During light loads, switch pulses are skipped to regulate the output and the quiescent current will be several mA. The SYNC pin may be tied high for spread spectrum modulation mode, and the LT8609/ LT8609A will operate similar to pulse-skipping mode but vary the clock frequency to reduce EMI. Comparators on the LT8609/LT8609A/LT8609B adjustable output parts monitoring the FB pin voltage will pull the PG pin low if the output voltage varies more than ±8.5% (typical) from the set point, or if a fault condition is present. Comparators on the LT8609A-3.3/LT8609A-5 fixed output parts monitoring the V OUT pin voltage will pull the PG pin low if the output voltage varies more than ±7.5% (typical) from the set point, or if a fault condition is present. The oscillator reduces the LT8609/LT8609A's operating frequency when the voltage at the FB pin is low, or the voltage at the V OUT pin is low on the LT8609A-3.3 or LT8609A-5 fixed voltage options. This frequency foldback helps to control the inductor current when the output voltage is lower than the programmed value which occurs during start-up. When a clock is applied to the SYNC pin the frequency foldback is disabled. The LT8609B has no SYNC pin and only operates in pulseskipping mode. ### APPLICATIONS INFORMATION ### Achieving Ultralow Quiescent Current To enhance efficiency at light loads, the LT8609/LT8609A enters into low ripple Burst Mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and minimizing output voltage ripple. In Burst Mode operation the LT8609/LT8609A delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor . While in sleep mode the LT8609/LT8609A consumes 1.7µA. As the output load decreases, the frequency of single current pulses decreases (see Figure 1) and the percentage of time the LT8609/LT8609A is in sleep mode increases, resulting in much higher light load efficiency than for typical converters. By maximizing the time between pulses, Figure 1b. Full Switching Frequency Minimum Load vs V IN in Pulse Skipping Mode the converter quiescent current approaches 2.5µA for a typical application when there is no output load. Therefore, to optimize the quiescent current performance at light loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current. While in Burst Mode operation the current limit of the top switch is approximately 600mA resulting in output voltage ripple shown in Figure 2. Increasing the output capacitance will decrease the output ripple proportionally. As load ramps upward from zero the switching frequency will increase but only up to the switching frequency programmed by the resistor at the RT pin as shown in Table 1. The output load at which the LT8609/LT8609A reaches the programmed frequency varies based on input voltage, output voltage, and inductor choice. For some applications, it is desirable for the LT8609/ LT8609A to operate in pulse-skipping mode, which is the only mode available to the LT8609B. Pulse-skipping mode offers two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. In this mode much of the internal circuitry is awake at all times, increasing quiescent current to several hundred µA. Second is that full switching frequency is reached at lower output load than in Burst Mode operation as shown in Figure 1b. To enable pulse-skipping mode the SYNC pin is floated. To achieve spread spectrum modulation with pulse-skipping mode, the SYNC pin is tied high. While a clock is applied to the SYNC pin the LT8609/LT8609A will also operate in pulse-skipping mode. ### FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the resistor values according to: ![Equation as printed (p. 15)](lt8609/figures/lt8609-eq01.png) $$R1=R2\left(\frac{V_{OUT}}{0.782V}-1\right)$$ *LaTeX transcription of the equation above, checked against the symbols printed on the page.* 1% resistors are recommended to maintain output voltage accuracy. The total resistance of the FB resistor divider should be selected to be as large as possible when good low load efficiency is desired: The resistor divider generates a small load on the output, which should be minimized to optimize the quiescent current at low loads. When using large FB resistors, a 10pF phase lead capacitor should be connected from V OUT to FB. The fixed output versions of the LT8609A have the feedback resistor network and phase lead capacitor integrated within the part. The FB pin is replaced with a V OUT pin for these regulators. The V OUT pin can be connected directly to the inductor and output capacitor. The LT8609A-3.3 regulates to 3.3V and has a total of 5.9M of internal feedback divider resistance from the V OUT pin to ground. The LT8609A-5 regulates to 5V and has a total of 8.95M of internal feedback divider resistance from the V OUT pin to ground. ### Setting the Switching Frequency The LT8609/LT8609A/LT8609B uses a constant frequency PWM architecture that can be programmed to switch from 200kHz to 2.2MHz by using a resistor tied from the RT pin to ground. A table showing the necessary R T value for a desired switching frequency is in Table 1. When in spread spectrum modulation mode, the frequency is modulated upwards of the frequency set by R T . **Table 1. SW Frequency vs RT Value** ([table-04-p15-data.csv](lt8609/tables/table-04-p15-data.csv), p. 15) | f_SW (MHz) | R_T (kΩ) | |---|---| | 0.2 | 221 | | 0.300 | 143 | | 0.400 | 110 | | 0.500 | 86.6 | | 0.600 | 71.5 | | 0.700 | 60.4 | | 0.800 | 52.3 | | 0.900 | 46.4 | | 1.000 | 40.2 | | 1.200 | 33.2 | | 1.400 | 27.4 | | 1.600 | 23.7 | | 1.800 | 20.5 | | 2.000 | 18.2 | | 2.200 | 16.2 | ### Operating Frequency Selection and T rade-Offs Selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. The advantage of high frequency operation is that smaller inductor and capacitor values may be used. The disadvantages are lower efficiency and a smaller input voltage range. The highest switching frequency (f SW(MAX) ) for a given application can be calculated as follows: ![Equation as printed (p. 15)](lt8609/figures/lt8609-eq02.png) $$f_{SW(MAX)} = \frac{V_{OUT} + V_{SW(BOT)}}{t_{ON(MIN)} \left( V_{IN} - V_{SW(TOP)} + V_{SW(BOT)} \right)}$$ *LaTeX transcription of the equation above, checked against the symbols printed on the page.* where V IN is the typical input voltage, V OUT is the output voltage, V SW(TOP) and V SW(BOT) are the internal switch drops (~0.4V, ~0.25V, respectively at max load) and t ON(MIN) is the minimum top switch on-time (see Typical Applications). This equation shows that slower switching frequency is necessary to accommodate a high V IN /V OUT ratio. For transient operation V IN may go as high as the Abs Max rating regardless of the RT value, however the LT8609/ LT8609A/LT8609B will reduce switching frequency as necessary to maintain control of inductor current to assure safe operation. The LT8609/LT8609A/LT8609B is capable of maximum duty cycle approaching 100%, and the V IN to V OUT dropout is limited by the R DS(ON) of the top switch. In this mode the LT8609/LT8609A /LT8609B skips switch cycles, resulting in a lower switching frequency than programmed by R T . For applications that cannot allow deviation from the programmed switching frequency at low V IN /V OUT ratios use the following formula to set switching frequency: ![Equation as printed (p. 16)](lt8609/figures/lt8609-eq03.png) where V IN(MIN) is the minimum input voltage without skipped cycles, V OUT is the output voltage, V SW(TOP) and VSW(BOT) are the internal switch drops (~0.4V, ~0.25V, respectively at max load), f SW is the switching frequency (set by RT), and t OFF(MIN) is the minimum switch offtime. Note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. ### Inductor Selection and Maximum Output Current The LT8609/LT8609A/LT8609B is designed to minimize solution size by allowing the inductor to be chosen based on the output load requirements of the application. During overload or short circuit conditions the LT8609/LT8609A/LT8609B safely tolerates operation with a saturated inductor through the use of a high speed peak-current mode architecture. A good first choice for the inductor value is: ![Equation as printed (p. 16)](lt8609/figures/lt8609-eq04.png) $$L = \frac{V_{OUT} + V_{SW ( BOT )}}{f_{SW}}$$ *LaTeX transcription of the equation above, checked against the symbols printed on the page.* where f SW is the switching frequency in MHz, V OUT is the output voltage, V SW(BOT) is the bottom switch drop (~0.25V) and L is the inductor value in µH. To avoid overheating and poor efficiency, an inductor must be chosen with an RMS current rating that is greater than the maximum expected output load of the application. In addition, the saturation current (typically labeled I SAT ) rating of the inductor must be higher than the load current plus 1/2 of in inductor ripple current: ![Equation as printed (p. 16)](lt8609/figures/lt8609-eq05.png) $$I_{L(PEAK)}=I_{LOAD(MAX)}+\frac{1}{2}\Delta_{L}$$ *LaTeX transcription of the equation above, checked against the symbols printed on the page.* where ∆I L is the inductor ripple current as calculated several paragraphs below and I LOAD(MAX) is the maximum output load for a given application. As a quick example, an application requiring 1A output should use an inductor with an RMS rating of greater than 1A and an I SAT of greater than 1.3A. To keep the efficiency high, the series resistance (DCR) should be less than 0.04Ω, and the core material should be intended for high frequency applications. The LT8609/LT8609A/LT8609B limits the peak switch current in order to protect the switches and the system from overload faults. The top switch current limit (I LIM ) is typically 4.75A at low duty cycles and decreases linearly to 4.0A at D = 0.8. The inductor value must then be sufficient to supply the desired maximum output current (I OUT(MAX) ), which is a function of the switch current limit (I LIM ) and the ripple current: ![Equation as printed (p. 16)](lt8609/figures/lt8609-eq06.png) $$I_{OUT(MAX)} = I_{LIM} - \frac{\Delta I_L}{2}$$ *LaTeX transcription of the equation above, checked against the symbols printed on the page.* The peak-to-peak ripple current in the inductor can be calculated as follows: ![Equation as printed (p. 16)](lt8609/figures/lt8609-eq07.png) $$\Delta I_L = \frac{V_{OUT}}{L \cdot f_{SW}} \left( 1 - \frac{V_{OUT}}{V_{IN(MAX)}} \right)$$ *LaTeX transcription of the equation above, checked against the symbols printed on the page.* where f SW is the switching frequency of the LT8609/ LT8609A/LT8609B, and L is the value of the inductor . Therefore, the maximum output current that the LT8609/ LT8609A/LT8609B will deliver depends on minimum the switch current limit, the inductor value, and the input and output voltages. The inductor value may have to be increased if the inductor ripple current does not allow sufficient maximum output current (I OUT(MAX) ) given the switching frequency, and maximum input voltage used in the desired application. The optimum inductor for a given application may differ from the one indicated by this design guide. A larger value inductor provides a higher maximum load current and reduces the output voltage ripple. For applications requiring smaller load currents, the value of the inductor may be lower and the LT8609/LT8609A/LT8609B may operate with higher ripple current. This allows use of a physically smaller inductor , or one with a lower DCR resulting in higher efficiency. Be aware that low inductance may result in discontinuous mode operation, which further reduces maximum load current. For more information about maximum output current and discontinuous operation, see Application Note 44. Finally, for duty cycles greater than 50% (V OUT /V IN > 0.5), a minimum inductance is required to avoid sub-harmonic oscillation. See Application Note 19. ### Input Capacitor Bypass the input of the LT8609/LT8609A/LT8609B circuit with a ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage, and should not be used. A 4.7µF to 10µF ceramic capacitor is adequate to bypass the LT8609/LT8609A/LT8609B and will easily handle the ripple current. Note that larger input capacitance is required when a lower switching frequency is used. If the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor . Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT8609/LT8609A/LT8609B and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 4.7µF capacitor is capable of this task, but only if it is placed close to the LT8609/LT8609A/ LT8609B (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT8609/LT8609A/ LT8609B. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8609/LT8609A/LT8609B circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8609/ LT8609A/LT8609B's voltage rating. This situation is easily avoided (see Analog Devices Application Note 88). ### Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor , it filters the square wave generated by the LT8609/LT8609A/LT8609B to produce the DC output. In this role it determines the output ripple, thus low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT8609/LT8609A/LT8609B's control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: ![Equation as printed (p. 17)](lt8609/figures/lt8609-eq08.png) $$C_{OUT} = \frac{100}{V_{OUT} \bullet f_{SW}}$$ *LaTeX transcription of the equation above, checked against the symbols printed on the page.* where f SW is in MHz, and C OUT is the recommended output capacitance in µF . Use X5R or X7R types. This choice will provide low output ripple and good transient response. Transient performance of adjustable output parts can be improved with a higher value output capacitor and the addition of a feedforward capacitor placed between V OUT and FB. Increasing the output capacitance will also decrease the output voltage ripple. A lower value of output capacitor can be used to save space and cost but transient performance will suffer and may cause loop instability. See the Typical Applications in this data sheet for suggested capacitor values. When choosing a capacitor , special attention should be given to the data sheet to calculate the effective capacitance under the relevant operating conditions of voltage bias and temperature. A physically larger capacitor or one with a higher voltage rating may be required. ### Ceramic Capacitors Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can cause problems when used with the LT8609/LT8609A/LT8609B due to their piezoelectric nature. When in Burst Mode operation, the LT8609/LT8609A/LT8609B's switching frequency depends on the load current, and at very light loads the LT8609/LT8609A/LT8609B can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT8609/LT8609A/LT8609B operates at a lower current limit during Burst Mode operation, the noise is typically very quiet to a casual ear . If this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output. A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LT8609/LT8609A/ LT8609B. As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8609/ LT8609A/LT8609B circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8609/LT8609A/LT8609B's rating. This situation is easily avoided (see Application Note 88). ### Enable Pin The LT8609/LT8609A/LT8609B is in shutdown when the EN pin is low and active when the pin is high. The rising threshold of the EN comparator is 1.05V, with 50mV of hysteresis. The EN pin can be tied to V IN if the shutdown feature is not used, or tied to a logic level if shutdown control is required. Adding a resistor divider from V IN to EN programs the LT8609/LT8609A/LT8609B to regulate the output only when V IN is above a desired voltage (see Block Diagram). Typically, this threshold, V IN(EN) , is used in situations where the input supply is current limited, or has a relatively high source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops. This looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. The V IN(EN) threshold prevents the regulator from operating at source voltages where the problems might occur . This threshold can be adjusted by setting the values R3 and R4 such that they satisfy the following equation: ![Equation as printed (p. 18)](lt8609/figures/lt8609-eq09.png) $$V_{IN ( EN )} = \left( \frac{R 3}{R 4} + 1 \right) \bullet 1 V$$ *LaTeX transcription of the equation above, checked against the symbols printed on the page.* where the LT8609/LT8609A/LT8609B will remain off until V IN is above V IN(EN) . Due to the comparator's hysteresis, switching will not stop until the input falls slightly below V IN(EN) . When in Burst Mode operation for light-load currents, the current through the V IN(EN) resistor network can easily be greater than the supply current consumed by the LT8609/LT8609A/LT8609B. Therefore, the V IN(EN) resistors should be large to minimize their effect on efficiency at low loads. ### INTV CC Regulator An internal low dropout (LDO) regulator produces the 3.5V supply from V IN that powers the drivers and the internal bias circuitry. The INTV CC can supply enough current for the LT8609/LT8609A/LT8609B's circuitry and must be bypassed to ground with a minimum of 1µF ceramic capacitor . Good bypassing is necessary to supply the high transient currents required by the power MOSFET gate drivers. Applications with high input voltage and high switching frequency will increase die temperature because of the higher power dissipation across the LDO. Do not connect an external load to the INTV CC pin. ### Output Voltage T racking and Soft-Start The LT8609/LT8609A/LT8609B allows the user to program its output voltage ramp rate by means of the TR/SS pin. An internal 2µA pulls up the TR/SS pin to INTV CC . Putting an external capacitor on TR/ SS enables soft-starting the output to prevent current surge on the input supply. During the soft-start ramp the output voltage will proportionally track the TR/SS pin voltage. For output tracking applications, TR/ SS can be externally driven by another voltage source. From 0V to 0.782V, the TR/SS voltage will override the internal 0.782V reference input to the error amplifier , thus regulating the FB pin voltage to that of TR/SS pin. In the LT8609A-3.3 and LT8609A-5 fixed output voltage options the output voltage will track the TR/SS pin voltage based on a factor set by the internal feedback resistor divider . The 3.3V output options will track to a voltage 4.2 times that of the TR/SS pin, while the 5V output options will track to a voltage 6.39 times that of the TR/SS pin. When TR/SS is above 0.782V, tracking is disabled and the feedback voltage will regulate to the internal reference voltage. An active pull-down circuit is connected to the TR/SS pin which will discharge the external soft-start capacitor in the case of fault conditions and restart the ramp when the faults are cleared. Fault conditions that clear the soft-start capacitor are the EN/UV pin transitioning low, V IN voltage falling too low, or thermal shutdown. ### Output Power Good When the LT8609/LT8609A/LT8609B's adjustable output voltage is within the ±8.5% window of the regulation point, which is a V FB voltage in the range of 0.716V to 0.849V (typical), the output voltage is considered good and the open-drain PG pin goes high impedance and is typically pulled high with an external resistor . Otherwise, the internal drain pull-down device will pull the PG pin low. To prevent glitching both the upper and lower thresholds include 0.5% of hysteresis. The LT8609A-3.3 and LT8609A-5 use a ±7.5% power good window around the regulation point, which for the 3.3V output version corresponds to a 3.0525V to 3.5475V range (typical) and for the 5V output version corresponds to a 4.625V to 5.375V range (typical). The PG pin is also actively pulled low during several fault conditions: EN/UV pin is below 1V, INTV CC has fallen too low, V IN is too low, or thermal shutdown. ### Synchronization To select low ripple Burst Mode operation, tie the SYNC pin below 0.4V (this can be ground or a logic low output). To synchronize the LT8609/LT8609A oscillator to an external frequency connect a square wave (with 20% to 80% duty cycle) to the SYNC pin. The square wave amplitude should have valleys that are below 0.9V and peaks above 2.7V (up to 5V). The LT8609/LT8609A will not enter Burst Mode operation at low output loads while synchronized to an external clock, but instead will pulse skip to maintain regulation. The LT8609/LT8609A may be synchronized over a 200kHz to 2.2MHz range. The R T resistor should be chosen to set the LT8609/LT8609A switching frequency equal to or below the lowest synchronization input. For example, if the synchronization signal will be 500kHz and higher , the R T should be selected for 500kHz. The slope compensation is set by the R T value, while the minimum slope compensation required to avoid subharmonic oscillations is established by the inductor size, input voltage, and output voltage. Since the synchronization frequency will not change the slopes of the inductor current waveform, if the inductor is large enough to avoid subharmonic oscillations at the frequency set by RT , then the slope compensation will be sufficient for all synchronization frequencies. For some applications, it is desirable for the LT8609/ LT8609A to operate in pulse-skipping mode, which is the only mode available to the LT8609B. Pulse-skipping mode offers two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. Second is that full switching frequency is reached at lower output load than in Burst Mode operation as shown in Figure 1b in an earlier section. These two differences come at the expense of increased quiescent current. To enable pulse-skipping mode the SYNC pin is floated. For some applications, reduced EMI operation may be desirable, which can be achieved through spread spectrum modulation. This mode operates similar to pulse skipping mode operation, with the key difference that the switching frequency is modulated up and down by a 3kHz triangle wave. The modulation has the frequency set by RT as the low frequency, and modulates up to approximately 20% higher than the frequency set by RT . To enable spread spectrum mode, tie SYNC to INTV CC or drive to a voltage between 3.2V and 5V. The LT8609/LT8609A/LT8609B does not operate in forced continuous mode regardless of SYNC signal. ### Shorted and Reversed Input Protection The LT8609/LT8609A/LT8609B will tolerate a shorted output. Several features are used for protection during output short-circuit and brownout conditions. The first is the switching frequency will be folded back while the output is lower than the set point to maintain inductor current control. Second, the bottom switch current is monitored such that if inductor current is beyond safe levels switching of the top switch will be delayed until such time as the inductor current falls to safe levels. This allows for tailoring the LT8609/LT8609A/LT8609B to individual applications and limiting thermal dissipation during short circuit conditions. Frequency foldback behavior depends on the state of the SYNC pin: If the SYNC pin is low or high, or floated the switching frequency will slow while the output voltage is lower than the programmed level. If the SYNC pin is connected to a clock source, the LT8609/LT8609A/LT8609B will stay at the programmed frequency without foldback and only slow switching if the inductor current exceeds safe levels. There is another situation to consider in systems where the output will be held high when the input to the LT8609/ LT8609A/LT8609B is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ORed with the LT8609/LT8609A/LT8609B's output. If the V IN pin is allowed to float and the EN pin is held high (either by a logic signal or because it is tied to V IN ), then the LT8609/ LT8609A/LT8609B's internal circuitry will pull its quiescent current through its SW pin. This is acceptable if the system can tolerate several µA in this state. If the EN pin is grounded the SW pin current will drop to near 0.7µA. However, if the V IN pin is grounded while the output is held high, regardless of EN, parasitic body diodes inside the LT8609/LT8609A/LT8609B can pull current from the output through the SW pin and the V IN pin. Figure 3 shows a connection of the V IN and EN/UV pins that will allow the LT8609/LT8609A/LT8609B to run only when the input voltage is present and that protects against a shorted or reversed input. ### PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 4 shows the recommended component placement with trace, ground plane and via locations. Note that large, switched currents flow in the LT8609/LT8609A/LT8609B's V IN pins, GND pins, and the input capacitor (C IN ). The loop formed by the input capacitor should be as small as possible by placing the capacitor adjacent to the V IN and GND pins. When using a physically large input capacitor the resulting loop may become too large in which case using a small case/value capacitor placed close to the VIN and GND pins plus a larger capacitor further away is preferred. These components, along with the inductor and output capacitor , should be placed on the same side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane under the application circuit on the layer closest to the surface layer . The SW and BOOST nodes should be as small as possible. Finally, keep the FB and RT nodes small so that the ground traces will shield them from the SW and BOOST nodes. The exposed pad on the bottom of the package must be soldered to ground so that the pad is connected to ground electrically and also acts as a heat sink thermally. To keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT8609/LT8609A/ LT8609B to additional ground planes within the circuit board and on the bottom side. ### Thermal Considerations and Peak Current Output For higher ambient temperatures, care should be taken in the layout of the PCB to ensure good heat sinking of the LT8609/LT8609A/LT8609B. The exposed pad on the bottom of the package must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias; these layers will spread heat dissipated by the LT8609/LT8609A/LT8609B. Placing additional vias can reduce thermal resistance further . The maximum load current should be derated as the ambient temperature approaches the maximum junction rating. Power dissipation within the LT8609/LT8609A/LT8609B can be estimated by calculating the total power loss from an efficiency measurement and subtracting the inductor loss. The die temperature is calculated by multiplying the LT8609/LT8609A/LT8609B power dissipation by the thermal resistance from junction to ambient. The LT8609/ LT8609A/LT8609B will stop switching and indicate a fault condition if safe junction temperature is exceeded. switching frequency. If the case temperature is too high for a given application, then either V IN , switching frequency or load current can be decreased to reduce the temperature to an acceptable level. Figure 5 shows how case temperature rise can be managed by reducing V IN . Temperature rise of the LT8609/LT8609A/LT8609B is worst when operating at high load, high V IN , and high Figure 6 shows an example of how case temperature rise changes with the duty cycle of a 10Hz pulsed 3A load. Junction temperature will be higher than case temperature. ### TYPICAL APPLICATIONS ### 3.3V Step-Down ### 5V Step-Down ### 12V Step-Down ### 1.8V 2MHz Step-Down Converter ### 3.3V 2MHz Step-Down Converter ### 5V 2MHz Step-Down Converter ### Ultralow EMI 5V 2A Step-Down Converter ### PACKAGE DESCRIPTION 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. BSC 2. DRAWING NOT TO SCALE ### MSE Package 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev F) 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. DDM Package 10-Lead Plastic Side Wettable DFN (3mm × (Reference LTC DWG # 05-08-1647 Rev Ø) ### 3mm) ### NOTE: 1. DRAWING NOT TO SCALE 2. ALL DIMENSIONS ARE IN MILLIMETERS 3. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 4. EXPOSED PAD SHALL BE SOLDER PLATED 5. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE BOTTOM VIEW-EXPOSED PAD ### REVISION HISTORY **Revision History** ([table-05-p28-data.csv](lt8609/tables/table-05-p28-data.csv), p. 28) | REV | DATE | DESCRIPTION | PAGE NUMBER | |---|---|---|---| | A | 01/16 | Added the LT8609A Version to Header | All | | | | Added the LT8609A Version to Description | 1 | | | | Clarified Description | 1 | | | | Clarified Electrical Specifications | 3 | | | | Clarified Load Regulation, Line Regulation, No-Load Supply Current vs Temperature, Minimum On-Time vs Temperature Graphs, Frequency Foldback and Soft-Start vs Temperature Graphs | 5, 6, 7, 8 | | | | Clarified Block Diagram with Optional Input Resistors | 10 | | | | Replaced Figure 1 with Table 1 in text | 12 | | | | Clarified C_IN Capacitor in Text and PCB Layout | 18 | | | | Clarified Typical Application | 24 | | B | 06/16 | Clarified Switch Drop vs Switch Current Graph axis units | 6 | | | | Clarified Switching Waveforms conditions | 8 | | C | 10/16 | Added LT8609B Option | All | | | | Added LT8609B Option to Absolute Maximum Ratings, Added LT8609B Package Drawing and Ordering Information | 2 | | | | Clarified Electrical Parameters and Notes for LT8609B Option | 3 | | | | Clarified Top FET Current Limit vs Temperature Graph | 6 | | | | Clarified Pin Functions to Include LT8609B | 10 | | | | Clarified Operation Section to Include LT8609B | 12 | | | | Clarified Applications Information Section to Include LT8609B | 13 – 20 | | | | Clarified Graphs in Figure 5 and 6 | 20 | | | | Clarified Typical Applications Schematics | 21, 22, 23, 24 | | D | 01/17 | Clarified Graphs | 6, 7, 20 | | | | Clarified Schematics | 23, 26 | | E | 06/17 | Add H-grade to the A version | 2, 4 | | | | Modified application circuits | 21, 22, 23 | | F | 11/17 | Clarified Oscillator Frequency R_T Conditions | 3 | | | | Clarified Minimum Off Time | 3 | | | | Clarified Efficiency Graph | 5 | | | | Clarified Frequency Foldback Graph | 8 | | | | Clarified Block Diagram | 11 | | | | Clarified Maximum Duty Cycle | 14 | | | | Clarified Figure 4 | 19 | | G | 01/18 | Added MSOP-16E Package option | 1, 2, 24 | | | | Clarified the Pin Functions | 10 | | H | 02/19 | Changed 2A/3A to 3A. | 1 | | | | Replaced all graphs with I_OUT to 3A. | 1, 5, 6, 7, 8 | | | | Added LT8609AJMSE16 and LT8609AJMSE options. | 2 | | | | Eliminated "The internal circuitry…" paragraph. | 15 | | | | Clarified Figure 4 PCB Layout. | 19 | | | | Clarified Figure 5. | 20 | | | | Eliminated "The LT8609/LT8609A/LT8609B's…" paragraph. | 20 | | | | Updated Typical Applications. | 21, 22 | | I | 01/20 | Added DFN version parts and J Grades. | 1, 2, 3 | | | | Clarified parametric table. | 4, 5 | | | | Added fixed output graphs. | 6, 7 ,8 | | | | Clarified Pin Functions. | 11 | | | | Clarified Block Diagram. | 12 | | | | Clarified Operation to include fixed output options. | 13 | | | | Added text for fixed output options. | 15 | | | | Added text in Output Capacitor and Output Ripple for fixed output options. | 17 | | | | Added text in Output Voltage Tracking section for fixed output options. | 18 | | | | Added text in Output Power Good section for fixed output options. | 19 | | | | Clarified Typical Applications. | 22-25 | | J | 08/21 | Clarified Output Reference Voltage for LT8609A-3.3 and Line Regulations under Electrical Characteristics table. | 4 | ### RELATED PARTS **Related Parts** ([table-06-p30-data.csv](lt8609/tables/table-06-p30-data.csv), p. 30) | PART NUMBER | DESCRIPTION | COMMENTS | |---|---|---| | LT8610A/ LT8610AB | 42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 2.5µA | V_IN = 3.4V to 42V, V_OUT(MIN) = 0.97V, I_Q = 2.5µA, I_SD < 1µA, MSOP-16E Package | | LT8610AC | 42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 2.5µA | V_IN = 3V to 42V, V_OUT(MIN) = 0.8V, I_Q = 2.5µA, I_SD < 1µA, MSOP-16E Package | | LT8610 | 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 2.5µA | V_IN = 3.4V to 42V, V_OUT(MIN) = 0.97V, I_Q = 2.5µA, I_SD < 1µA, MSOP-16E Package | | LT8611 | 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 2.5µA and Input/Output Current Limit/Monitor | V_IN = 3.4V to 42V, V_OUT(MIN) = 0.97V, I_Q = 2.5µA, I_SD < 1µA, 3mm × 5mm QFN-24 Package | | LT8616 | 42V, Dual 2.5A + 1.5A, 95% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 5µA | V_IN = 3.4V to 42V, V_OUT(MIN) = 0.8V, I_Q = 5µA, I_SD < 1µA, TSSOP-28E, 3mm × 6mm QFN-28 Packages | | LT8620 | 65V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 2.5µA | V_IN = 3.4V to 65V, V_OUT(MIN) = 0.97V, I_Q = 2.5µA, I_SD < 1µA, MSOP-16E, 3mm × 5mm QFN-24 Packages | | LT8614 | 42V, 4A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 2.5µA | V_IN = 3.4V to 42V, V_OUT(MIN) = 0.97V, I_Q = 2.5µA, I_SD < 1µA, 3mm × 4mm QFN-18 Package | | LT8612 | 42V, 6A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 2.5µA | V_IN = 3.4V to 42V, V_OUT(MIN) = 0.97V, I_Q = 3.0µA, I_SD < 1µA, 3mm × 6mm QFN-28 Package | | LT8640 | 42V, 5A/7A Peak, 96% Efficiency, 3MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 2.5µA | V_IN = 3.4V to 42V, V_OUT(MIN) = 0.97V, I_Q = 2.5µA, I_SD < 1µA, 3mm × 4mm QFN-18 Package | | LT8602 | 42V, Quad Output (2.5A+1.5A+1.5A+1.5A) 95% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I_Q = 25µA | V_IN = 3V to 42V, V_OUT(MIN)= 0.8V, I_Q = 25µA, I_SD < 1µA, 6mm × 6mm QFN-40 Package | ## Additional Figures ![application circuit (p. 1)](lt8609/figures/lt8609-f000.png) ![12VIN to 5VOUT Efficiency](lt8609/figures/lt8609-f001.png) *12VIN to 5VOUT Efficiency* ![pinout (p. 2)](lt8609/figures/lt8609-f002.png) ![LT8609 Efficiency (3.3V Output, Burst Mode Operation) (8609 G01)](lt8609/figures/lt8609-f004.png) *LT8609 Efficiency (3.3V Output, Burst Mode Operation) (8609 G01)* ![LT8609 Efficiency (5V Output, Burst Mode Operation) (8609 G04)](lt8609/figures/lt8609-f005.png) *LT8609 Efficiency (5V Output, Burst Mode Operation) (8609 G04)* ![LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) (8609 G07)](lt8609/figures/lt8609-f006.png) *LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) (8609 G07)* ![LT8609 Efficiency (3.3V Output, Burst Mode Operation) (8609 G02)](lt8609/figures/lt8609-f007.png) *LT8609 Efficiency (3.3V Output, Burst Mode Operation) (8609 G02)* ![LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) (8609 G05)](lt8609/figures/lt8609-f008.png) *LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) (8609 G05)* ![LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) (8609 G08)](lt8609/figures/lt8609-f009.png) *LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) (8609 G08)* ![LT8609 Efficiency (5V Output, Burst Mode Operation) (8609 G03)](lt8609/figures/lt8609-f010.png) *LT8609 Efficiency (5V Output, Burst Mode Operation) (8609 G03)* ![LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) (8609 G06)](lt8609/figures/lt8609-f011.png) *LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) (8609 G06)* ![FB Voltage](lt8609/figures/lt8609-f012.png) *FB Voltage* ![LT8609A-3.3 VOUT Voltage](lt8609/figures/lt8609-f013.png) *LT8609A-3.3 VOUT Voltage* ![LT8609A-5 VOUT Voltage](lt8609/figures/lt8609-f014.png) *LT8609A-5 VOUT Voltage* ![Line Regulation](lt8609/figures/lt8609-f015.png) *Line Regulation* ![No-Load Supply Current Tested in Regulation](lt8609/figures/lt8609-f016.png) *No-Load Supply Current Tested in Regulation* ![Top FET Current Limit vs Duty Cycle](lt8609/figures/lt8609-f017.png) *Top FET Current Limit vs Duty Cycle* ![Load Regulation](lt8609/figures/lt8609-f018.png) *Load Regulation* ![No-Load Supply Current vs Temperature (N ot Switching)](lt8609/figures/lt8609-f019.png) *No-Load Supply Current vs Temperature (N ot Switching)* ![Top FET Current Limit vs Temperature](lt8609/figures/lt8609-f020.png) *Top FET Current Limit vs Temperature* ![Switch Drop vs Temperature](lt8609/figures/lt8609-f021.png) *Switch Drop vs Temperature* ![Minimum On-Time vs Temperature](lt8609/figures/lt8609-f022.png) *Minimum On-Time vs Temperature* ![Dropout Voltage vs Load Current](lt8609/figures/lt8609-f023.png) *Dropout Voltage vs Load Current* ![Switch Drop vs Switch Current](lt8609/figures/lt8609-f024.png) *Switch Drop vs Switch Current* ![Minimum Off-Time vs Temperature](lt8609/figures/lt8609-f025.png) *Minimum Off-Time vs Temperature* ![Switching Frequency vs Temperature](lt8609/figures/lt8609-f026.png) *Switching Frequency vs Temperature* ![Burst Frequency vs Load Current](lt8609/figures/lt8609-f027.png) *Burst Frequency vs Load Current* ![Minimum Load to Full Frequency (SYNC Float to 1.9V)](lt8609/figures/lt8609-f028.png) *Minimum Load to Full Frequency (SYNC Float to 1.9V)* ![Soft-Start Tracking](lt8609/figures/lt8609-f029.png) *Soft-Start Tracking* ![Soft-Start Current vs Temperature](lt8609/figures/lt8609-f030.png) *Soft-Start Current vs Temperature* ![Case Temperature vs Load Current](lt8609/figures/lt8609-f031.png) *Case Temperature vs Load Current* ![Frequency Foldback](lt8609/figures/lt8609-f032.png) *Frequency Foldback* ![VIN UVLO](lt8609/figures/lt8609-f033.png) *VIN UVLO* ![Case Temperature vs 3A Pulsed Load](lt8609/figures/lt8609-f034.png) *Case Temperature vs 3A Pulsed Load* ![Switching Waveforms (8609 G33)](lt8609/figures/lt8609-f036.png) *Switching Waveforms (8609 G33)* ![Switching Waveforms (8609 G34)](lt8609/figures/lt8609-f037.png) *Switching Waveforms (8609 G34)* ![Transient Response (8609 G36)](lt8609/figures/lt8609-f038.png) *Transient Response (8609 G36)* ![Start-Up Dropout (8609 G38)](lt8609/figures/lt8609-f039.png) *Start-Up Dropout (8609 G38)* ![Switching Waveforms (8609 G35)](lt8609/figures/lt8609-f040.png) *Switching Waveforms (8609 G35)* ![Transient Response (8609 G37)](lt8609/figures/lt8609-f041.png) *Transient Response (8609 G37)* ![Start-Up Dropout (8609 G39)](lt8609/figures/lt8609-f042.png) *Start-Up Dropout (8609 G39)* ![block diagram (p. 12)](lt8609/figures/lt8609-f043.png) ![unclassified image (p. 14)](lt8609/figures/lt8609-f044.png) ![Figure 1a. SW Burst Mode Frequency vs Load](lt8609/figures/lt8609-f045.png) *Figure 1a. SW Burst Mode Frequency vs Load* ![Figure 2. Burst Mode Operation](lt8609/figures/lt8609-f046.png) *Figure 2. Burst Mode Operation* ![Figure 3. Reverse V IN Protection](lt8609/figures/lt8609-f047.png) *Figure 3. Reverse V IN Protection* ![Figure 4. PCB Layout](lt8609/figures/lt8609-f048.png) *Figure 4. PCB Layout* ![Figure 5. Case Temperature Rise vs Load Current](lt8609/figures/lt8609-f049.png) *Figure 5. Case Temperature Rise vs Load Current* ![application circuit (p. 22)](lt8609/figures/lt8609-f050.png) ![characteristic curve (p. 22)](lt8609/figures/lt8609-f051.png) ![Figure 6. Case Temperature Rise vs 3A Pulsed Load](lt8609/figures/lt8609-f052.png) *Figure 6. Case Temperature Rise vs 3A Pulsed Load* ![application circuit (p. 23)](lt8609/figures/lt8609-f053.png) ![application circuit (p. 23)](lt8609/figures/lt8609-f054.png) ![application circuit (p. 23)](lt8609/figures/lt8609-f055.png) ![application circuit (p. 24)](lt8609/figures/lt8609-f056.png) ![application circuit (p. 24)](lt8609/figures/lt8609-f057.png) ![MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I)](lt8609/figures/lt8609-f058.png) *MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I)* ![other (p. 26)](lt8609/figures/lt8609-f059.png) ![other (p. 27)](lt8609/figures/lt8609-f060.png) ![other (p. 27)](lt8609/figures/lt8609-f061.png) ![other (p. 27)](lt8609/figures/lt8609-f062.png) ![RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS](lt8609/figures/lt8609-f063.png) *RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS* ![Tracking 3.3V and 1.8V 2MHz Converters](lt8609/figures/lt8609-f064.png) *Tracking 3.3V and 1.8V 2MHz Converters* ## Additional Tables - **Absolute Maximum Ratings** — [table-01-p2-abs_max.csv](lt8609/tables/table-01-p2-abs_max.csv), p. 2