POWER LOSS (mW) LTC3857 Low I , Dual, 2-Phase Q Synchronous Step-Down Controller FEATURES DESCRIPTION n The LTC 3857 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 (40V Abs Max) 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 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 Independent TRACK/SS pins for each controller ramp the n Adjustable Output Voltage Soft-Start or Tracking output voltages during start-up. Current foldback limits n Power Good Output Voltage Monitors MOSFET heat dissipation during short-circuit conditions. n Output Overvoltage Protection The PLLIN/MODE pin selects among Burst Mode opera- n Low Shutdown I : <8A Q tion, pulse-skipping mode, or continuous inductor current n Internal LDO Powers Gate Drive from V or EXTV IN CC mode at light loads. n No Current Foldback During Start-up n 5mm 5mm QFN Package For a leaded 28-lead SSOP package with a fixed current limit and one PGOOD output, without phase modulation APPLICATIONS or a clock output, see the LTC3857-1 data sheet. n Automotive Always-On Systems L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, PolyPhase, Module, Linear Technology and the Linear logo are registered trademarks and No R and UltraFast are trademarks of Linear SENSE n Battery Operated Digital Devices Technology Corporation. All other trademarks are the property of their respective owners. n Protected by U.S. Patents, including 5481178, 5929620, 6177787, 6144194, 5408150, Distributed DC Power Systems 6580258, 5705919, 6100678. TYPICAL APPLICATION Efficiency and Power Loss High Efficiency Dual 3.3V/8.5V Step-Down Converter V IN vs Output Current 9V TO 38V 22F 100 10000 4.7F 50V V = 12V IN V INTV IN CC 90 V = 3.3V OUT TG1 TG2 FIGURE 13 CIRCUIT 80 1000 0.1F 0.1F BOOST1 BOOST2 3.3H 7.2H 70 SW1 SW2 60 100 BG1 BG2 50 LTC3857 PGND 40 10 + + SENSE1 SENSE2 30 0.007 0.010 20 1 V 10 V SENSE1 SENSE2 OUT2 OUT1 8.5V 3.3V V V FB1 FB2 0 0.1 3.5A 5A 62.5k 193k I I 0.00001 0.0001 0.001 0.01 0.1 1 10 TH1 TH2 150F 680pF 680pF 150F OUTPUT CURRENT (A) TRACK/SS1 SGND TRACK/SS2 20k 3857 TA01b 20k 15k 15k 0.1F 0.1F 3857 TA01 3857fd 1 EFFICIENCY (%)LTC3857 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Input Supply Voltage (V ) ......................... 0.3V to 40V IN Topside Driver Voltages BOOST1, BOOST2 ................................. 0.3V to 46V Switch Voltage (SW1, SW2) ........................ 5V to 40V 32 31 30 29 28 27 26 25 SENSE1 1 24 BOOST1 PLLIN/MODE, (BOOST1-SW1), (BOOST2-SW2), FREQ 2 23 BG1 INTV ........................................................ 0.3V to 6V CC PHASMD 3 22 V IN RUN1, RUN2 ................................................ 0.3V to 8V CLKOUT 4 21 PGND 33 Maximum Current Sourced into Pin SGND PLLIN/MODE 5 20 EXTV CC from Source >8V...............................................100A SGND INTV 6 19 CC + + SENSE1 , SENSE2 , SENSE1 RUN1 7 18 BG2 SENSE2 Voltages ...................................... 0.3V to 28V RUN2 8 17 BOOST2 9 10 11 12 13 14 15 16 FREQ Voltages ..................................... 0.3V to INTV CC I , PHASMD Voltages ....................... 0.3V to INTV LIM CC EXTV ...................................................... 0.3V to 14V CC I , I ,V , V Voltages ...................... 0.3V to 6V TH1 TH2 FB1 FB2 UH PACKAGE 32-LEAD (5mm s 5mm) PLASTIC QFN PGOOD1, PGOOD2 Voltages ....................... 0.3V to 6V T = 125C, = 34C/W JMAX JA TRACK/SS1, TRACK/SS2 Voltages .............. 0.3V to 6V EXPOSED PAD (PIN 33) IS SGND, MUST BE SOLDERED TO PCB Operating Junction Temperature Range (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 LTC3857EUH PBF LTC3857EUH TRPBF 3857 32-Lead (5mm 5mm) Plastic QFN 40C to 125C LTC3857IUH PBF LTC3857IUH TRPBF 3857 40C to 125C 32-Lead (5mm 5mm) Plastic QFN 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: