Features

• Wide V_IN Range: 4V to 38V Operation
• R_SENSE or DCR Current Sensing
• ±1% Output Voltage Accuracy
• Power Good Output Voltage Monitor
• Phase-Lockable Fixed Frequency: 250kHz to 750kHz
• Dual N-Channel MOSFET Synchronous Drive
• Very Low Dropout Operation: 99% Duty Cycle
• Adjustable Output Voltage Soft-Start or Tracking
• Output Current Foldback Limiting
• Output Overvoltage Protection
• OPTI-LOOP® Compensation Minimizes C_OUT
• Selectable Continuous, Pulse-Skipping or Burst Mode® Operation at Light Loads
• Low Shutdown I_Q: 20μA
• V_OUT Range: 0.8V to 5.5V
• Thermally Enhanced 16-Lead MSOP or 3mm × 3mm QFN Package

Typical Application

Description

The LTC3851A-1 is a high performance synchronous step-down switching regulator controller that drives an all N-channel synchronous power MOSFET stage. A constant frequency current mode architecture allows a phase‑lockable frequency of up to 750kHz.

OPTI-LOOP compensation allows the transient response to be optimized over a wide range of output capacitance and ESR values. The LTC3851A-1 features a precision 0.8V reference and a power good indicator. A wide 4V to 38V (40V absolute maximum) input supply range encompasses most battery configurations and intermediate bus voltages.

The TK/SS pin ramps the output voltage during start‑up and shutdown with coincident or ratiometric tracking. Current foldback limits MOSFET heat dissipation during shortcircuit conditions. The MODE/PLLIN pin selects among Burst Mode operation, pulse-skipping mode or continuous inductor current mode at light loads and allows the IC to be synchronized to an external clock. The LTC3851A-1 contains an improved PLL compared to the LTC3851-1.

The LTC3851A-1 is identical to the LTC3851A except that the ILIM pin is replaced by PGOOD.