POWER LOSS (W) LTC3708 Fast 2-Phase, No R SENSE Buck Controller with Output Tracking FEATURES DESCRIPTION n Very Low Duty Factor Operation (t < 85ns) The LTC 3708 is a dual, 2-phase synchronous step-down ON(MIN) n No R Option for Maximum Efficiency switching regulator with output voltage up/down tracking SENSE n Very Fast Transient Response capability. The IC allows either coincident or ratiometric n Programmable Output Voltage Up/Down Tracking tracking. Multiple LTC3708s can be daisy-chained in ap- n 2-Phase Operation Reduces Input Capacitance plications requiring more than two voltages to be tracked. n 0.6V 1% Output Voltage Reference Power supply sequencing is accomplished using an ex- n External Frequency Synchronization ternal soft-start timing capacitor. n Monotonic Soft-Start The LTC3708 uses a constant on-time, valley current n Onboard High Current MOSFET Drivers mode control architecture to deliver very low duty factors n Wide V Range: Up to 36V IN without requiring a sense resistor. Operating frequency is n Adjustable Cycle-by-Cycle Current Limit selected by an external resistor and is compensated for n Instant Output Overvoltage Protection variations in input supply voltage. An internal phase-locked n Optional Short-Circuit Shutdown Timer loop allows the IC to be synchronized to an external clock. n Power Good Output with 100s Masking n Fault protection is provided by an output overvoltage Available in 5mm 5mm QFN Package comparator and an optional short-circuit shutdown timer. The regulator current limit level is user programmable. A APPLICATIONS wide supply range allows voltages as high as 36V to be n Digital Signal Processors stepped down to 0.6V output. n Network Servers L, LT, LTC, LTM, Linear Technology, the Linear logo and PolyPhase are registered trademarks and No R is a trademark of Linear Technology Corporation. All other trademarks are the SENSE property of their respective owners. TYPICAL APPLICATION High Efficiency Dual Output Step-Down Converter V (0.5V/DIV) OUT1 V IN 3.3V TO 28V V (0.5V/DIV) OUT2 5V 10F 50V 4 1F 4.7F 10 100k V DRV PGOOD CC CC M1 TG1 TG2 M2 L1 L2 3708 TA01b BOOST1 BOOST2 2ms/DIV 1.4H 1.2H V V OUT1 0.22F 0.22F OUT2 SW2 2.5V SW1 1.8V + + + + 15A POSCAP SENSE2 POSCAP 15A B340A SENSE1 B340A 100 9.0 330F 470F 4V M3 BG1 LTC3708 BG2 M4 2.5V 95 7.5 2 2 SENSE2 SENSE1 12.1k 19.1k PGND1 PGND2 12.1k 90 6.0 V V FB1 FB2 TRACK2 FCB f IN 1M 85 4.5 V V I I IN IN ON1 ON2 20V TO 2.5V IN OUT 1.5M I I TH1 TH2 5V TO 2.5V IN OUT 80 3.0 INTLPF EXTLPF 20V TO 1.8V IN OUT 5V TO 1.8V RUN/SS TRACK1 IN OUT 6.04k 6.04k 33k 6.04k 10k 1k 33k SGND V V 75 1.5 RNG1 RNG2 100k 0.01F 0.01F 0.1F 0.01F 70 0 180pF 25k 180pF 0.1F 0.01 0.1 1 10 5V LOAD CURRENT (A) 3708 TA01 L1: PANASONIC ETQP3HIR4BF M1, M2: RENESAS HAT2168 3708 TA01c L2: PANASONIC ETQP2HIR2BF M3, M4: RENESAS HAT2165 3708fc 1 For more information www.linear.com/LTC3708 EFFICIENCY (%) +LTC3708 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Input Supply Voltage (V , DRV ) ............. 7V to 0.3V CC CC Boosted Topside Driver Supply Voltage BOOST1, 2 ............................................ 42V to 0.3V 32 31 30 29 28 27 26 25 Switch Voltage (SW1, 2) .............................. 36V to 5V RUN/SS 1 24 SENSE1 + + SENSE1 , SENSE2 Voltages ........................ 36V to 5V I 2 23 PGND1 TH1 SENSE1 , SENSE2 Voltages .................... 10V to 0.3V V 3 22 BG1 FB1 I , I Voltages .................................... 21V to 0.3V ON1 ON2 TRACK1 4 21 DRV CC 33 (BOOST SW) Voltages .............................. 7V to 0.3V SGND 5 20 BG2 RUN/SS, PGOOD Voltages .......................... 7V to 0.3V TRACK2 PGND2 6 19 V 7 18 SENSE2 PGOOD DC Current ................................................. 5mA FB2 I 8 17 V TH2 CC TRACK1, TRACK2 Voltages ..............V + 0.3V to 0.3V CC 9 10 11 12 13 14 15 16 V , V Voltages.................... V + 0.3V to 0.3V RNG1 RNG2 CC I , I Voltages ................................... 2.7V to 0.3V TH1 TH2 V , V Voltages .................................. 2.7V to 0.3V FB1 FB2 UH PACKAGE INTLPF, EXTLPF Voltages ........................ 2.7V to 0.3V 32-LEAD (5mm 5mm) PLASTIC QFN FCB Voltages ............................................... 7V to 0.3V T = 125C, = 34C/W JMAX JA EXPOSED PAD (PIN 33) IS SGND, MUST BE SOLDERED TO PCB Operating Temperature Range (Note 5) ...40C to 85C Junction Temperature (Note 2) ........................... 125C Storage Temperature Range .................. 65C to 125C Reflow Peak Body Temperature ........................... 260C ORDER INFORMATION