Low I, 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.

LTC3857

LTC3857-1

Features

Adjustable Current Limit, Clock Output, Phase Modulation, 2 PGOOD Outputs

Fixed Current Limit, One PGOOD Output

Package

QFN-32

SSOP-28

Applications

* Automotive Always-On Systems

* Battery Operated Digital Devices

* Distributed DC Power Systems

* 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