LT8641A

65V, 3.5A/5A Peak Synchronous Step-Down Silent Switcher with 2.5μA Quiescent Current

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EVAL-LT8641A-AZ - Demo Manual

Overview

Features and Benefits
Product Details

Features and Benefits

Silent Switcher^® Architecture
- Ultralow EMI Emissions
- Spread Spectrum Frequency Modulation
High Efficiency at High Frequency
- Up to 95% Efficiency at 1MHz, 12V_IN to 5V_OUT
- Up to 94% Efficiency at 2MHz, 12V_IN to 5V_OUT
Wide Input Voltage Range: 3V to 65V
3.5A Maximum Continuous, 5A Peak Transient Output
Ultralow Quiescent Current Burst Mode^® Operation
- 2.5μA I_Q Regulating 12V_IN to 3.3V_OUT
- Output Ripple < 10mV_P-P

Fast Minimum Switch On-Time: 35ns
- True 2MHz Operation for 24V_IN Systems
Low Dropout Under All Conditions: 130mV at 1A
Safely Tolerates Inductor Saturation in Overload
Adjustable and Synchronizable: 200kHz to 3MHz
Output Soft-Start and Tracking
Small 18-Lead 3mm × 4mm Side Wettable QFN with Improved Solder Joint Reliability
AEC-Q100 Qualified for Automotive Applications

Product Details

The LT8641A step-down regulator features Silent Switcher architecture designed to minimize EMI emissions while delivering high efficiency at frequencies up to 3MHz. Assembled in a 3mm × 4mm side wettable QFN, the monolithic construction with integrated power switches and inclusion of all necessary circuitry yields a solution with a minimal PCB footprint. An ultralow 2.5μA quiescent current — with the output in full regulation — enables applications requiring highest efficiency at very small load currents. Transient response remains excellent and output voltage ripple is below 10m_VP-P at any load, from zero to full current.

The LT8641A allows high V_IN to low V_OUT conversion at high frequency with a fast minimum top switch on-time of 35ns. Operation is safe in overload even with a saturated inductor.

Essential features are included and easy to use: an open-drain PG pin signals when the output is in regulation. The SYNC/MODE pin selects between Burst Mode, pulse-skipping, or spread spectrum mode, and also allows synchronization to an external clock. Soft-start and tracking functionality are accessed through the TR/SS pin. An accurate enable threshold can be set using the EN/UV pin and a resistor at the RT pin programs switch frequency.

APPLICATIONS

Automotive and Industrial Supplies
General Purpose Step-Down

Product Categories

Power Management
- Internal Power Switch Buck Regulators
- High Input Voltage Buck Regulators

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Product Lifecycle Recommended for New Designs

This product has been released to the market. The data sheet contains all final specifications and operating conditions. For new designs, ADI recommends utilization of these products.

Evaluation Kits (1)

EVAL-LT8641A

65V, 3.5A/5A Peak Synchronous Step-Down Silent Switcher

EVAL-LT8641A

View Detailed Evaluation Kit Information

Evaluation circuit EVAL-LT8641A-AZ is a 65V, 3.5A/5A peak synchronous step-down Silent Switcher^® with spread spectrum frequency modulation featuring the LT8641A. The demo board is designed for 5V output from a 5.5V to 65V input. The wide input range allows a variety of input sources, such as automotive batteries and industrial supplies. The LT8641A is a compact, ultralow emission, high efficiency, high speed synchronous monolithic step-down switching regulator. Top and bottom power switches, compensation components, and other necessary circuits inside the LT8641A minimize external components and simplify design. The special Silent Switcher architecture minimizes EMI emissions. The selectable spread spectrum mode can further improve EMI performance. Ultralow 2.5μA quiescent current in Burst Mode^® operation achieves high efficiency at very light loads. Fast minimum on-time of 35ns enables high V_IN to low V_OUT conversion at high frequency.

The LT8641A switching frequency can be programmed either through oscillator resistor or external clock over a 200kHz to 3MHz range. The default frequency of the evaluation board is 2MHz. The SYNC pin on the evaluation board is grounded by JP1 for low ripple burst mode operation. Move JP1 to PULSE SKIPPING position
to change the operation mode to pulse-skipping operation. Once JP1 is on SPREAD SPECTRUM position, V_CC is applied to the SYNC pin for low EMI spread spectrum operation. To synchronize to an external clock, move JP1 to SYNC and apply the external clock to the SYNC turret. Figure 1 in the user guide shows the efficiency of the circuit at 12V and 24V input in Burst Mode operation.

Figure 2 in the user guide shows EMI performances of the board (with EMIfilter). The red lines in Figure 2 are CISPR25 Class5 peak limit. The figure shows that the circuit passes the test with a wide margin. To achieve EMI/EMC performance, as shown in Figure 2, the input EMI filter is required, and the input voltage should be applied at the VEMI turret.

The LT8641A data sheet gives a complete description of the part, operation, and application information. Read the data sheet in conjunction with the user guide for EVAL-LT8641A-AZ. The LT8641A is assembled in a 3mm × 4mm plastic QFN package with exposed pad for low thermal resistance. The layout recommendations for low EMI operation and maximum thermal performance are available in the “Low EMI PCB Layout and Thermal Considerations” and “Peak Output Current” sections of the data sheet.

Resources

EVAL-LT8641A-AZ - Demo Manual (Rev. 0)

PDF

761.3 K

Documentation & Resources

Data Sheets

LT8641A: 65V, 3.5A/5A Peak Synchronous Step-Down Silent Switcher with 2.5μA Quiescent Current Data Sheet (Rev. 0)
5/8/2023

PDF

855 K

User Guides

EVAL-LT8641A-AZ - Demo Manual (Rev. 0)
5/8/2023

PDF

761K

Tools & Simulations

LTspice

LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.

LTspice downloads and documentation

Models for the following parts are available in LTspice:

LT8641

LTpowerCAD

LTpowerCAD^® is a power supply design program which selects power stage components, provides detailed power efficiency, shows quick loop Bode plot stability and load transient analysis, and can export to LTspice for simulation.

LTpowerCAD download and documentation

Design tools for the following parts are available in LTpowerCAD:

LT8641

Design Resources

ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.View our quality and reliability program and certifications for more information.

Part Number	Material Declaration	Reliability Data	Pin/Package Drawing	CAD Symbols, Footprints & 3D Models
LT8641ARUDCM#PBF	Material Declaration	Reliability Data	20(18)-Lead Plastic Side Wettable QFN (3mm × 4mm)	Ultra Librarian SamacSys
LT8641ARUDCM#TRPBF	Material Declaration	Reliability Data	20(18)-Lead Plastic Side Wettable QFN (3mm × 4mm)	Ultra Librarian SamacSys
LT8641ARUDCM#WPBF	Material Declaration	Reliability Data	20(18)-Lead Plastic Side Wettable QFN (3mm × 4mm)	Ultra Librarian SamacSys
LT8641ARUDCM#WTRPBF	Material Declaration	Reliability Data	20(18)-Lead Plastic Side Wettable QFN (3mm × 4mm)	Ultra Librarian SamacSys
Wafer Fabrication Data

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Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.