Features

• Dual, 180° Phased Controllers Reduce Required Input Capacitance and Power Supply Induced Noise
• OPTI-LOOP Compensation Minimizes C_OUT
• ±1.5% Output Voltage Accuracy
• Power Good Output Voltage Indicator
• Phase-Lockable Fixed Frequency 250kHz to 550kHz
• Over Current Latchoff Disabled
• Wide VIN Range: 4.5V to 28V (35V for LTC3728LI-1) Operation
• Very Low Dropout Operation: 99% Duty Cycle
• Adjustable Soft-Start Current Ramping
• Foldback Output Current Limiting
• Output Overvoltage Protection
• Low Shutdown I_Q: 20μA
• 5V and 3.3V Standby Regulators
• 3 Selectable Operating Modes: Constant Frequency, Burst Mode Operation and PWM
• 5mm × 5mm QFN and 28-Lead Narrow SSOP Packages

Typical Application

Description

The LTC3728L-1 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. The LTC3728L-1 is identical to the LTC3728L except that the LTC3728L-1 lacks the over current latchoff feature.

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 microproces- sor generations, and a wide 4.5V to 28V (30V maximum/ 35V for LTC3728LI-1) input supply range encompasses all battery chemistries.

A RUN/SS pin for each controller provides soft-start. Current foldback limits MOSFET dissipation during short- circuit conditions. The FCB mode pin can select among Burst Mode operation, constant frequency mode and continuous inductor current mode or regulate a secondary winding. The LTC3728L-1 includes a power good output pin that indicates when both outputs are within 7.5% of their designed set point.