LTC1778/LTC1778-1 Wide Operating Range, TM No R Step-Down Controller SENSE FEATURES DESCRIPTIO No Sense Resistor Required The LTC 1778 is a synchronous step-down switching True Current Mode Control regulator controller optimized for CPU power. The con- Optimized for High Step-Down Ratios troller uses a valley current control architecture to deliver t 100ns very low duty cycles with excellent transient response ON(MIN) Extremely Fast Transient Response without requiring a sense resistor. Operating frequency is Stable with Ceramic C selected by an external resistor and is compensated for OUT Dual N-Channel MOSFET Synchronous Drive variations in V . IN Power Good Output Voltage Monitor (LTC1778) Discontinuous mode operation provides high efficiency Adjustable On-Time (LTC1778-1) operation at light loads. A forced continuous control pin Wide V Range: 4V to 36V IN reduces noise and RF interference, and can assist second- 1% 0.8V Voltage Reference ary winding regulation by disabling discontinuous opera- Adjustable Current Limit tion when the main output is lightly loaded. Adjustable Switching Frequency Fault protection is provided by internal foldback current Programmable Soft-Start limiting, an output overvoltage comparator and optional Output Overvoltage Protection short-circuit shutdown timer. Soft-start capability for sup- Optional Short-Circuit Shutdown Timer ply sequencing is accomplished using an external timing Micropower Shutdown: I < 30A Q capacitor. The regulator current limit level is user program- Available in a 16-Pin Narrow SSOP Package mable. Wide supply range allows operation from 4V to 36V U APPLICATIO S at the input and from 0.8V up to (0.9)V at the output. IN , LTC and LT are registered trademarks of Linear Technology Corporation. Notebook and Palmtop Computers No R is a trademark of Linear Technology Corporation. SENSE All other trademarks are the property of their respective owners. Distributed Power Systems Protected by U.S. Patents, including 5481178, 6100678, 6580258, 5847554, 6304066 TYPICAL APPLICATIO R ON Efficiency vs Load Current 1.4M I ON 100 C SS V = 2.5V V OUT IN 0.1F V IN V = 5V 5V TO 28V IN C IN M1 RUN/SS TG 10F Si4884 L1 90 50V C C 1.8H SW V 3 OUT 500pF C 0.22F 2.5V V = 25V B IN I C BOOST OUT 10A TH + D B 180F R C 80 LTC1778 CMDSH-3 4V 20k SGND INTV 2 CC M2 D1 BG Si4874 B340A + 70 C VCC 4.7F R2 PGOOD PGND 30.1k 60 V FB 0.01 0.1 1 10 R1 LOAD CURRENT (A) 14k 1778 F01b 1778 F01a Figure 1. High Efficiency Step-Down Converter 1778fb 1 EFFICIENCY (%) U ULTC1778/LTC1778-1 ABSOLUTE AXI U RATI GS (Note 1) Input Supply Voltage (V , I )................. 36V to 0.3V TG, BG, INTV , EXTV Peak Currents.................... 2A CC CC IN ON Boosted Topside Driver Supply Voltage TG, BG, INTV , EXTV RMS Currents .............. 50mA CC CC (BOOST) ................................................... 42V to 0.3V Operating Ambient Temperature Range (Note 4) SW Voltage .................................................. 36V to 5V LTC1778E ........................................... 40C to 85C EXTV , (BOOST SW), RUN/SS, LTC1778I.......................................... 40C to 125C CC PGOOD Voltages....................................... 7V to 0.3V Junction Temperature (Note 2)............................ 125C FCB, V , V Voltages .......... INTV + 0.3V to 0.3V Storage Temperature Range ................. 65C to 150C ON RNG CC I , V Voltages...................................... 2.7V to 0.3V Lead Temperature (Soldering, 10 sec).................. 300C TH FB UU W PACKAGE/ORDER I FOR ATIO TOP VIEW TOP VIEW ORDER PART ORDER PART RUN/SS 1 NUMBER RUN/SS 1 NUMBER 16 BOOST 16 BOOST PGOOD 2 15 V 2 15 TG TG ON LTC1778EGN LTC1778EGN-1 V 3 14 V 3 14 SW SW RNG RNG LTC1778IGN FCB 4 13 FCB 4 13 PGND PGND I 5 12 I 5 12 BG BG TH TH SGND 6 11 SGND 6 11 INTV INTV CC CC GN PART MARKING GN PART MARKING I 7 10 I 7 10 V V ON IN ON IN V 8 9 V 8 9 EXTV EXTV FB CC FB CC 1778 17781 GN PACKAGE GN PACKAGE 1778I 16-LEAD PLASTIC SSOP 16-LEAD PLASTIC SSOP T = 125C, = 130C/ W T = 125C, = 130C/ W JMAX JA JMAX JA Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are T = 25C. V = 15V unless otherwise noted. A IN SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loop I Input DC Supply Current Q Normal 900 2000 A Shutdown Supply Current 15 30 A V Feedback Reference Voltage I = 1.2V (Note 3) LTC1778E 0.792 0.800 0.808 V FB TH I = 1.2V (Note 3) LTC1778I 0.792 0.800 0.812 V TH V Feedback Voltage Line Regulation V = 4V to 30V, I = 1.2V (Note 3) 0.002 %/V FB(LINEREG) IN TH V Feedback Voltage Load Regulation I = 0.5V to 1.9V (Note 3) 0.05 0.3 % FB(LOADREG) TH I Feedback Input Current V = 0.8V 5 50 nA FB FB g Error Amplifier Transconductance I = 1.2V (Note 3) 1.4 1.7 2 mS m(EA) TH V Forced Continuous Threshold 0.76 0.8 0.84 V FCB I Forced Continuous Pin Current V = 0.8V 1 2 A FCB FCB t On-Time I = 30A, V = 0V (LTC1778-1) 198 233 268 ns ON ON ON I = 15A, V = 0V (LTC1778-1) 396 466 536 ns ON ON t Minimum On-Time I = 180A 50 100 ns ON(MIN) ON 1778fb 2 U WWW