Datasheet LTC3857-1 (Analog Devices)

LTC3857-1 Low IQ, Dual, 2-Phase Synchronous Step-Down Controller
FEATURES DESCRIPTION
n
Low Operating IQ: 50μA (One Channel On)
The LTC®3857-1 is a high performance dual step-down n
Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 24V
switching regulator controller that drives all N-channel n
Wide VIN Range: 4V to 38V
synchronous power MOSFET stages. A constant frequency n
RSENSE or DCR Current Sensing
current mode architecture allows a phase-lockable fre- n Out-of-Phase Controllers Reduce Required Input quency of up to 850kHz. Power loss and noise due to the Capacitance and Power Supply Induced Noise ESR of the input capacitor ESR are minimized by operating n OPTI-LOOP® Compensation Minimizes COUT the two controller output stages out of phase. n Phase-Lockable Frequency (75kHz-850kHz) The 50μA no-load quiescent current extends operating life n Programmable Fixed Frequency (50kHz-900kHz) in battery-powered systems. The LTC3857-1 features a n Selectable Continuous, Pulse-Skipping or Low Ripple precision 0.8V reference and a power good output indicator. Burst Mode® Operation at Light Loads A wide 4V to 38V input supply range encompasses a wide n Very Low Dropout Operation: 99% Duty Cycle range of intermediate bus voltages and battery chemistries. n Adjustable Output Voltage Soft-Start or Tracking n Power Good Output Voltage Monitor Independent TRACK/SS pins for each controller ramp the n Output Overvoltage Protection output voltages during start-up. Current foldback limits n Low Shutdown I MOSFET heat dissipation during short-circuit conditions. Q: <8μA n Internal LDO Powers Gate Drive from V The PLLIN/MODE pin selects among Burst Mode opera- IN or EXTVCC n No Current Foldback During Start-Up tion, pulse-skipping mode, or continuous inductor current n Narrow SSOP Package mode at light loads.
APPLICATIONS
For a leadless 32-pin QFN package with the additional fea- tures of adjustable current limit, clock out, phase modula- n Automotive Always-On Systems tion and two PGOOD outputs, see the LTC3857 data sheet. n Battery Operated Digital Devices L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, μModule, Linear Technology and the Linear logo are registered trademarks and No R n Distributed DC Power Systems SENSE and UltraFast are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 5929620, 6177787, 6144194, 5408150, 6580258, 5705919, 6100678.
TYPICAL APPLICATION High Efficiency Dual 3.3V/8.5V Step-Down Converter
VIN
Efficiency and Power Loss
9V TO 38V 22μF
vs Output Current
1μF 50V VIN INTVCC 100 10000 V TG1 TG2 IN = 12V 90 V 0.1μF 0.1μF OUT = 3.3V FIGURE 13 CIRCUIT 3.3μH BOOST1 BOOST2 7.2μH 80 1000 SW1 SW2 POWER LOSS (mW) 70 BG1 BG2 60 100 LTC3857-1 PGND 50 SENSE1+ SENSE2+ 40 10 EFFICIENCY (%) 0.007Ω 0.010Ω 30 20 1 V V OUT1 SENSE1– SENSE2– OUT2 3.3V 8.5V VFB1 VFB2 10 5A 62.5k I 193k 3.5A TH1 ITH2 0 0.1 150μF 680pF 680pF TRACK/SS1 TRACK/SS2 150μF SGND 20k 0.00001 0.0001 0.001 0.01 0.1 1 10 20k 15k 15k OUTPUT CURRENT (A) 0.1μF 0.1μF 3857 TA01b 38571 TA01 38571fc 1 Document Outline FEATURES DESCRIPTION APPLICATIONS TYPICAL APPLICATION ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDER INFORMATION ELECTRICAL CHARACTERISTICS TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS FUNCTIONAL DIAGRAM OPERATION APPLICATIONS INFORMATION TYPICAL APPLICATIONS PACKAGE DESCRIPTION REVISION HISTORY TYPICAL APPLICATION RELATED PARTS