Features and Benefits
- Dual, 180° Phased Controllers Reduce Required Input Capacitance and Power Supply Induced Noise
- OPTI-LOOP® Compensation Minimizes COUT
- ±1% Output Voltage Accuracy
- Power Good Output Voltage Indicator
- Phase-Lockable Fixed Frequency 250kHz to 550kHz
- Dual N-Channel MOSFET Synchronous Drive
- Wide VIN Range: 3.5V to 36V Operation
- Very Low Dropout Operation: 99% Duty Cycle
- Adjustable Soft-Start Current Ramping
- Foldback Output Current Limiting
- Latched Short-Circuit Shutdown with Defeat Option
- Output Overvoltage Protection
- Remote Output Voltage Sense
- Low Shutdown IQ : 20µA
- 5V and 3.3V Regulators
- 3 Selectable Operating Modes: Constant-Frequency, Burst Mode® Operation and PWM
- Available in 32-Pin 5mm x 5mm QFN and 28-Pin SSOP Packages
The LTC3728 is a dual high performance step-down switching regulator controller that drives all N-channel synchronous power MOSFET stages. A constant-frequency current mode architecture allows phase-lockable frequency of up to 550kHz. Power loss and noise due to the ESR of the input capacitors are minimized by operating the two controller output stages out of phase.
OPTI-LOOP compensation allows the transient response to be optimized over a wide range of output capacitance and ESR values. The precision 0.8V reference and power good output indicator are compatible with future microprocessor generations, and a wide 3.5V to 30V (36V maximum) input supply range encompasses all battery chemistries.
A RUN/SS pin for each controller provides both softstart and optional timed, short-circuit shutdown. Current foldback limits MOSFET dissipation during short-circuit conditions when overcurrent latchoff is disabled. Output overvoltage protection circuitry latches on the bottom MOSFET until VOUT returns to normal. The FCB mode pin can select among Burst Mode, constant-frequency mode and continuous inductor current mode or regulate a secondary winding. The LTC3728 includes a power good output pin that indicates when both outputs are within 7.5% of their designed set point.
|Vin Range||Vref Accy||Current Limit Latch Off||3.3V LDO Available|
|LTC3728||3.5V to 36V||+/-1%||Yes|
|LTC3728L||4.5V to 28V||+/-1%||Yes||Yes|
|LTC3728LX||4.5V to 28V||+/- 1.5%||Yes||Yes|
|LTC3728L-1||4.5V to 28V||+/- 1.5%||Foldback only||Yes|
- Notebook and Palmtop Computers
- Telecom Systems
- Portable Instruments
- Battery-Operated Digital Devices
- DC Power Distribution Systems
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Evaluation Kits (3)
Demonstration circuit 542 is a dual output, dual phase synchronous step-down controller, featuring the LTC3728EG. Output #1 can be configured for either 5.0V or 3.3V and output #2 can be configured for either 3.3V or 2.5V. The maximum load for both rails is 12A. The input voltage range of the DC542 is 8V to 24V. The DC542 also contains a footprint for a 5.5V boost converter bias supply whose output is connected to EXTVCC. See the “Optional Bias Supply” section for more details.
Demonstration circuit 447 is a step-down converter featuring the LTC3728EUH regulator. The PolyPhase® dual output controller LTC3728EUH drives two high current synchronous buck converters. Input is 5V–14V, output 1 is 2.5V with loads up to 13A and output 2 is 1.8V with loads up to 13A. For applications with input voltage less than 5V, DC447 includes a circuit footprint on the bottom side to provide a 5V bias power supply.
Demonstration circuit 392 is a dual output, step-down, synchronous buck converter featuring either the 150kHz to 300kHz LTC1628EUH controller (DC392A-A), the 250kHz to 550kHz LTC3728EUH (DC392A-B) or 250kHz to 550kHz LTC3728LUH (DC392A-C). It operates with an input voltage range of 7V to 24V and provides 3.3V @ 5A and 5V @ 4A at its output.
Tools & Simulations
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Models for the following parts are available in LTspice:
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Sample & Buy
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