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 (LTC1628-PG)
• DC Programmed 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
• Small 28-Lead SSOP Package
• Selectable Constant Frequency or Burst Mode® Operation
• Available in 5mm x 5mm QFN and 28-Pin SSOP Packages

Typical Application

Description

The LTC1628/LTC1628-PG are high performance dual step-down switching regulator controllers that drive all N-channel synchronous power MOSFET stages. A constant frequency current mode architecture allows adjustment of the frequency 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. The LTC1628-PG includes a power good output pin that replaces the FLTCPL, fault coupling control pin of the LTC1628.