Datasheet LTC3857 (Analog Devices)

LTC3857 Low IQ, Dual, 2-Phase Synchronous Step-Down Controller
FEATURES DESCRIPTION
n
Low Operating IQ: 50μA (One Channel On)
The LTC®3857 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 (40V Abs Max)
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 run n Programmable Fixed Frequency (50kHz-900kHz) time in battery-powered systems. The LTC3857 features a n Selectable Continuous, Pulse-Skipping or Low Ripple precision 0.8V reference and power good output indicators. Burst Mode® Operation at Light Loads A wide 4V to 38V input supply range encompasses a wide n Selectable Current Limit range of intermediate bus voltages and battery chemistries. n Very Low Dropout Operation: 99% Duty Cycle n Adjustable Output Voltage Soft-Start or Tracking Independent TRACK/SS pins for each controller ramp the n Power Good Output Voltage Monitors output voltages during start-up. Current foldback limits n Output Overvoltage Protection MOSFET heat dissipation during short-circuit conditions. n Low Shutdown I The PLLIN/MODE pin selects among Burst Mode opera- Q : <8μA n Internal LDO Powers Gate Drive from V tion, pulse-skipping mode, or continuous inductor current IN or EXTVCC n No Current Foldback During Start-up mode at light loads. n 5mm × 5mm QFN Package For a leaded 28-lead SSOP package with a fixed current
APPLICATIONS
limit and one PGOOD output, without phase modulation or a clock output, see the LTC3857-1 data sheet. n Automotive Always-On Systems L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, PolyPhase, μModule, Linear Technology and the n Battery Operated Digital Devices Linear logo are registered trademarks and No RSENSE and UltraFast are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. n Distributed DC Power Systems 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 Efficiency and Power Loss
VIN
vs Output Current
9V TO 38V 22μF 4.7μF 50V 100 10000 VIN = 12V VIN INTVCC 90 VOUT = 3.3V TG1 TG2 FIGURE 13 CIRCUIT 0.1μF 0.1μF 80 1000 3.3μH BOOST1 BOOST2 POWER LOSS (mW) 7.2μH 70 SW1 SW2 60 100 BG1 BG2 50 LTC3857 PGND 40 10 EFFICIENCY (%) SENSE1+ SENSE2+ 30 0.007Ω 0.010Ω 20 1 V V 10 OUT1 SENSE1– SENSE2– OUT2 3.3V 8.5V VFB1 VFB2 0 0.1 5A 62.5k I 193k 3.5A TH1 ITH2 0.00001 0.0001 0.001 0.01 0.1 1 10 150μF 680pF 680pF TRACK/SS1 TRACK/SS2 150μF SGND OUTPUT CURRENT (A) 20k 20k 15k 15k 3857 TA01b 0.1μF 0.1μF 3857 TA01 3857fd 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