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LTC3857 - Low IQ, Dual, 2-Phase Synchronous Step-Down Controller

The LTC3857 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 run time in battery-powered systems. The LTC3857 features a precision 0.8V reference and power good output indicators. A 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 leaded 28-lead SSOP package with a fixed current limit and one PGOOD output, without phase modulation or a clock output, see the LTC3857-1 data sheet.

Features Low Operating IQ: 50μA (One Channel On) Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 24V Wide VIN Range: 4V to 38V (40V Abs Max) RSENSE or DCR Current Sensing Out-of-Phase Controllers Reduce Required Input Capacitance and Power Supply Induced Noise OPTI-LOOP® Compensation Minimizes COUT Phase-Lockable Frequency (75kHz-850kHz) Programmable Fixed Frequency (50kHz-900kHz) Selectable Continuous, Pulse-Skipping or Low Ripple Burst Mode® Operation at Light Loads Selectable Current Limit Very Low Dropout Operation: 99% Duty Cycle Adjustable Output Voltage Soft-Start or Tracking Power Good Output Voltage Monitors Output Overvoltage Protection Low Shutdown IQ : <8μA Internal LDO Powers Gate Drive from VIN or EXTVCC No Current Foldback During Start-up 5mm × 5mm QFN Package Typical Application

Applications Automotive Always-On Systems Battery Operated Digital Devices Distributed DC Power Systems Packaging

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