Features

• Low Operating I_Q: 50μA (One Channel On)
• Wide Output Voltage Range: 0.8V ≤ V_OUT ≤ 24V
• Wide V_IN Range: 4V to 38V
• R_SENSE or DCR Current Sensing
• Out-of-Phase Controllers Reduce Required Input Capacitance and Power Supply Induced Noise
• OPTI-LOOP® Compensation Minimizes C_OUT
• Phase-Lockable Frequency (75kHz-850kHz)
• Programmable Fixed Frequency (50kHz-900kHz)
• Selectable Continuous, Pulse-Skipping or Low Ripple Burst Mode® Operation at Light Loads
• Very Low Dropout Operation: 99% Duty Cycle
• Adjustable Output Voltage Soft-Start or Tracking
• Power Good Output Voltage Monitor
• Output Overvoltage Protection
• Low Shutdown I_Q: <8μA
• Internal LDO Powers Gate Drive from V_IN or EXTV_CC
• No Current Foldback During Start-Up
• Narrow SSOP Package

Typical Application

Description

The LTC3857-1 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 a phase-lockable frequency of up to 850kHz. Power loss and noise due to the ESR of the input capacitor ESR are minimized by operating the two controller output stages out of phase.

The 50μA no-load quiescent current extends operating life in battery-powered systems. The LTC3857-1 features a precision 0.8V reference and a power good output indicator. wide 4V to 38V input supply range encompasses a wide range of intermediate bus voltages and battery chemistries.

Independent TRACK/SS pins for each controller ramp the output voltages during start-up. Current foldback limits MOSFET heat dissipation during short-circuit conditions. The PLLIN/MODE pin selects among Burst Mode operation, pulse-skipping mode, or continuous inductor current mode at light loads.

For a leadless 32-pin QFN package with the additional features of adjustable current limit, clock out, phase modulation and two PGOOD outputs, see the LTC3857 data sheet.