Features

• Out-of-Phase Controllers Reduce Required Input Capacitance and Power Supply Induced Noise
• OPTI-LOOP^® Compensation Minimizes C_OUT
• Dual N-Channel MOSFET Synchronous Drive
• ±1% Output Voltage Accuracy
• Power Good Output Voltage Monitor
• Phase-Lockable Fixed Frequency 150kHz to 300kHz
• Wide V_IN 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 I_Q: 20µA
• 5V and 3.3V Standby Regulators
• Selectable Constant Frequency or Burst Mode™ Operation
• Small 28-Lead SSOP Package

Typical Application

Description

The LTC®1628-SYNC is a high performance dual 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 300kHz. 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 soft-start 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 V_OUT 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.