LTC3720 Single Phase VRM8.5 Current Mode Step-Down Controller FEATURES DESCRIPTIO n 5-Bit Programmable Output Voltage: The LTC 3720 is a synchronous step-down switching 1.05V to 1.825V (VRM8.5) regulator controller for CPU power. An output voltage n between 1.05V and 1.825V is selected by a 5-bit code No Sense Resistor Required n 2% to 87% Duty Cycle at 200kHz (Intel VRM8.5 VID specification). The controller uses a n t 100ns valley current control architecture to deliver very low duty ON(MIN) n cycles without requiring a sense resistor. Operating fre- Supports Active Voltage Positioning n True Current Mode Control quency is selected by an external resistor and is compen- n Stable with Ceramic C sated for variations in V and V . OUT IN OUT n Dual N-Channel MOSFET Synchronous Drive Discontinuous mode operation provides high efficiency n Power Good Output Voltage Monitor operation at light loads. A forced continuous control pin n Wide V Range: 4V to 36V IN reduces noise and RF interference and can assist second- n 1% 0.8V Reference ary winding regulation by disabling discontinuous mode n Adjustable Current Limit operation when the main output is lightly loaded. n Adjustable Switching Frequency Fault protection is provided by internal foldback current n Forced Continuous Control Pin limiting, an output overvoltage comparator and optional n Programmable Soft-Start short-circuit shutdown timer. Soft-start capability for sup- n Output Overvoltage Protection ply sequencing is accomplished using an external timing n Optional Short-Circuit Shutdown Timer capacitor. The regulator current limit level is also user n Micropower Shutdown: I < 30m A Q programmable. Wide supply range allows operation from n Available in 28-Lead Narrow SSOP Package 4V to 36V at the input. U , LTC and LT are registered trademarks of Linear Technology Corporation. APPLICATIO S No R is a trademark of Linear Technology Corporation. SENSE Pentium is a registered trademark of Intel Corporation. n Power Supplies for Pentium Processors n Notebook Computers and Servers TYPICAL APPLICATIO LTC3720 330k Efficiency vs Output Current PGOOD I ON 100 V IN V = 1.45V 0.1F V OUT IN 5V TO 24V L1 = 1H 95 IRF7811W 10F RUN/SS TG 2 L1 5 90 470pF 1H V = 5V I SW V IN TH OUT 1.05V TO 1.825V 85 20k 0.33F C SGND BOOST OUT 20A + V = 15V 80 IN 270F V CMDSH-3 CC 2V 75 INTV 4 CC UPS840 + + VID4 SENSE 70 4.7F IRF7811W VID3 C : CORNELL DUBILIER BG OUT 3 65 ESRE271M02B 5-BIT VID VID2 PGND L1: SUMIDA CEP125-IROMC 60 VID1 SENSE 3720 F01a VID0 V OSENSE 55 0.01 1 10 100 0.1 OUTPUT CURRENT (A) 3720 F01b Figure 1. High Efficiency Step-Down Converter 3720f 1 EFFICIENCY (%) U ULTC3720 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART TOP VIEW Input Supply Voltage NUMBER 1 28 BOOST V , I ..................................................36V to 0.3V RUN/SS IN ON V 2 27 TG ON Boosted Topside Driver Supply Voltage LTC3720EGN PGOOD 3 26 SW BOOST.................................................. 42V to 0.3V + 4 25 SENSE V RNG + SW, SENSE Voltages ................................. 36V to 5V FCB 5 24 SENSE EXTV , (BOOST SW), RUN/SS, V CC CC I 6 23 PGND TH 7 BG VID0-VID4, PGOOD Voltages ..................... 7V to 0.3V SGND 22 8 21 INTV I CC ON FCB, V , V Voltages .......... INTV + 0.3V to 0.3V ON RNG CC V 9 20 V IN FB I , V , V Voltages....................... 2.7V to 0.3V TH FB OSENSE 10 EXTV SGND 19 CC TG, BG, INTV , EXTV Peak Currents.................... 2A CC CC 11 18 V V FB CC TG, BG, INTV , EXTV RMS Currents .............. 50mA CC CC V 12 17 VID4 OSENSE Operating Ambient Temperature Range VID0 13 16 VID3 14 15 VID2 VID1 LTC3720EGN (Note 2) ........................ 40 C to 85 C GN PACKAGE Junction Temperature (Note 3)............................ 125 C 28-LEAD NARROW PLASTIC SSOP Storage Temperature Range ................. 65 C to 150 C T = 125 C, q = 95 C/ W JMAX JA Lead Temperature (Soldering, 10 sec).................. 300 C Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The l denotes specifications which apply over the full operating temperature range, otherwise specifications are T = 25 C. 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 m A Shutdown Supply Current 15 30 m A V Feedback Reference Voltage I = 1.2V (Note 4) l 0.792 0.800 0.808 V FB TH D V Feedback Voltage Line Regulation V = 4V to 30V, I = 1.2V (Note 4) 0.002 %/V FB(LINEREG) IN TH D V Feedback Voltage Load Regulation I = 0.5V to 1.9V (Note 4) l 0.05 0.3 % FB(LOADREG) TH I Feedback Pin Input Current 5 50 nA FB g Error Amplifier Transconductance I = 1.2V (Note 4) 1.4 1.7 2 mS m(EA) TH V Forced Continuous Threshold l 0.76 0.8 0.84 V FCB I Forced Continuous Pin Current V = 0.8V 1 2 m A FCB FCB t On-Time I = 60m A, V = 1.5V 200 250 300 ns ON ON ON I = 30m A, V = 1.5V 425 500 575 ns ON ON t Minimum On-Time I = 180m A, V = 0V 50 100 ns ON(MIN) ON ON t Minimum Off-Time I = 60m A, V = 1.5V 250 400 ns OFF(MIN) ON ON V Maximum Current Sense Threshold V = 1V, V = 0.76V l 113 133 153 mV SENSE(MAX) RNG FB + V V V = 0V, V = 0.76V l 79 93 107 mV SENSE SENSE RNG FB V = INTV , V = 0.76V l 158 186 214 mV RNG CC FB V Minimum Current Sense Threshold V = 1V, V = 0.84V 67 mV SENSE(MIN) RNG FB + V V V = 0V, V = 0.84V 47 mV SENSE SENSE RNG FB V = INTV , V = 0.84V 93 mV RNG CC FB D V Output Overvoltage Fault Threshold 5.5 7.5 9.5 % FB(OV) V Output Undervoltage Fault Threshold 520 600 680 mV FB(UV) V RUN Pin Start Threshold l 0.8 1.5 2 V RUN/SS(ON) 3720f 2 U WWW