POWER LOSS (mW) LTC3857-1 Low I , Dual, 2-Phase Q Synchronous Step-Down Controller FEATURES DESCRIPTION n The LTC 3857-1 is a high performance dual step-down Low Operating I : 50A (One Channel On) Q n switching regulator controller that drives all N-channel Wide Output Voltage Range: 0.8V V 24V OUT n synchronous power MOSFET stages. A constant frequency Wide V Range: 4V to 38V IN n current mode architecture allows a phase-lockable fre- R or DCR Current Sensing SENSE n quency of up to 850kHz. Power loss and noise due to the Out-of-Phase Controllers Reduce Required Input ESR of the input capacitor ESR are minimized by operating Capacitance and Power Supply Induced Noise n the two controller output stages out of phase. OPTI-LOOP Compensation Minimizes C OUT n Phase-Lockable Frequency (75kHz-850kHz) The 50A 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 Independent TRACK/SS pins for each controller ramp the n Power Good Output Voltage Monitor output voltages during start-up. Current foldback limits n Output Overvoltage Protection MOSFET heat dissipation during short-circuit conditions. n Low Shutdown I : <8A Q The PLLIN/MODE pin selects among Burst Mode opera- n Internal LDO Powers Gate Drive from V or EXTV IN CC tion, pulse-skipping mode, or continuous inductor current n No Current Foldback During Start-Up mode at light loads. n Narrow SSOP Package For a leadless 32-pin QFN package with the additional fea- APPLICATIONS tures of adjustable current limit, clock out, phase modula- n tion and two PGOOD outputs, see the LTC3857 data sheet. Automotive Always-On Systems n L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Module, Linear Technology and the Linear logo Battery Operated Digital Devices are registered trademarks and No R and UltraFast are trademarks of Linear Technology SENSE n Distributed DC Power Systems 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 V Efficiency and Power Loss IN 9V TO 38V 22F vs Output Current 1F 50V 100 10000 V INTV IN CC V = 12V IN TG1 TG2 90 V = 3.3V OUT 0.1F 0.1F FIGURE 13 CIRCUIT BOOST1 BOOST2 3.3H 7.2H 80 1000 SW1 SW2 70 BG1 BG2 60 100 LTC3857-1 PGND 50 + + SENSE1 40 10 SENSE2 30 0.007 0.010 20 1 V V SENSE1 SENSE2 OUT2 OUT1 8.5V 3.3V V V 10 FB1 FB2 3.5A 5A 62.5k 193k I I TH1 TH2 0 0.1 150F 680pF 680pF 150F 0.00001 0.0001 0.001 0.01 0.1 1 10 TRACK/SS1 SGND TRACK/SS2 20k OUTPUT CURRENT (A) 20k 15k 15k 0.1F 0.1F 3857 TA01b 38571 TA01 38571fc 1 EFFICIENCY (%)LTC3857-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Input Supply Voltage (V ) ......................... 0.3V to 40V IN Topside Driver Voltages 1 28 TRACK/SS1 I TH1 2 27 PGOOD1 BOOST1, BOOST2 ................................. 0.3V to 46V V FB1 + 3 26 TG1 SENSE1 Switch Voltage (SW1, SW2) ........................ 5V to 40V 4 25 SW1 SENSE1 (BOOST1-SW1), (BOOST2-SW2), INTV ... 0.3V to 6V CC 5 24 BOOST1 FREQ RUN1, RUN2 ................................................ 0.3V to 8V 6 23 BG1 PLLIN/MODE Maximum Current Sourced into Pin 7 22 V SGND IN from Source >8V...............................................100A 8 21 PGND RUN1 + + SENSE1 , SENSE2 , SENSE1 9 20 EXTV RUN2 CC SENSE2 Voltages ...................................... 0.3V to 28V 10 19 INTV SENSE2 CC PLLIN/MODE, FREQ Voltages .............. 0.3V to INTV + CC 11 18 BG2 SENSE2 EXTV ...................................................... 0.3V to 14V CC 12 17 BOOST2 V FB2 I , I ,V , V Voltages ...................... 0.3V to 6V 13 16 SW2 TH1 TH2 FB1 FB2 I TH2 PGOOD1 Voltage ......................................... 0.3V to 6V 14 15 TG2 TRACK/SS2 TRACK/SS1, TRACK/SS2 Voltages .............. 0.3V to 6V GN PACKAGE 28-LEAD PLASTIC SSOP Operating Junction Temperature Range T = 125C, = 90C/W JMAX JA (Note 2) .................................................. 40C to 125C Maximum Junction Temperature (Note 3) ............ 125C Storage Temperature Range ................... 65C to 150C ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3857EGN-1 PBF LTC3857EGN-1 TRPBF LTC3857GN-1 28-Lead Plastic SSOP 40C to 125C LTC3857IGN-1 PBF LTC3857IGN-1 TRPBF LTC3857GN-1 28-Lead Plastic SSOP 40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: