LTC3717 Wide Operating Range, TM No R Step-Down Controller SENSE for DDR/QDR Memory Termination FEATURES DESCRIPTIO n V = 1/2 V (Supply Splitter) OUT IN The LTC 3717 is a synchronous step-down switching n Adjustable and Symmetrical Sink/Source regulator controller for double data rate (DDR) and Quad TM TM Current Limit up to 20A Data Rate (QDR ) memory termination. The controller n 0.65% Output Voltage Accuracy uses a valley current control architecture to deliver very n Up to 97% Efficiency low duty cycles without requiring a sense resistor. Oper- n No Sense Resistor Required ating frequency is selected by an external resistor and is n Ultrafast Transient Response compensated for variations in V . IN n True Current Mode Control Forced continuous operation reduces noise and RF inter- n 2% to 90% Duty Cycle at 200kHz ference. Output voltage is internally set to half of V , REF n t 100ns ON(MIN) which is user programmable. n Stable with Ceramic C OUT n Dual N-Channel MOSFET Synchronous Drive Fault protection is provided by an output overvoltage n Power Good Output Voltage Monitor comparator and optional short-circuit shutdown timer. n Wide V Range: 4V to 36V Soft-start capability for supply sequencing is accom- CC n Adjustable Switching Frequency up to 1.5MHz plished using an external timing capacitor. The regulator n Output Overvoltage Protection current limit level is symmetrical and user programmable. n Optional Short-Circuit Shutdown Timer Wide supply range allows operation from 4V to 36V at the n Available in a 16-Pin Narrow SSOP Package V input. CC U , LTC and LT are registered trademarks of Linear Technology Corporation. APPLICATIO S No R is a trademark of Linear Technology Corporation. SENSE QDR RAMs and Quad Data Rate RAMs comprise a new family of products developed by Cypress Semiconductor, Hitachi, IDT, Micron Technology, Inc. and Samsung. n Bus Termination: DDR and QDR Memory, SSTL, HSTL, ... n Notebook Computers, Desktop Servers n Tracking Power Supply TYPICAL APPLICATIO V CC Efficiency vs Load Current R ON 5V TO 28V 715k 1F V V 100 CC IN I ON V = 1.25V 2.5V TO 5.5V OUT + C 90 IN V V = 2.5V REF DD 150F V = 5V 80 IN M1 D2 6.3V RUN/SS TG Si7840DP B320A 2 70 V = 2.5V C IN C C SS SW V OUT 470pF 0.1F 60 1.25V C 0.22F B L1 C I BOOST 10A TH OUT + 50 D 0.68H 180F R B C LTC3717 CMDSH-3 4V 20k 40 SGND INTV 2 CC M2 D1 30 BG Si7840DP B320A + 20 C VCC 4.7F 10 PGOOD PGND 0 0 2 4 6 8 10 12 14 V FB 3717 F01a LOAD CURRENT (A) 3717 F01b Figure 1. High Efficiency DDR Memory Termination Supply sn3717 3717fs 1 EFFICIENCY (%) U ULTC3717 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART Input Supply Voltage (V , I ) .................36V to 0.3V CC ON TOP VIEW NUMBER Boosted Topside Driver Supply Voltage RUN/SS 1 16 BOOST (BOOST) ................................................... 42V to 0.3V LTC3717EGN PGOOD 2 15 TG SW Voltage .................................................. 36V to 5V V 3 14 SW RNG EXTV , (BOOST SW), RUN/SS, CC I 4 13 PGND TH PGOOD Voltages....................................... 7V to 0.3V 5 SGND 12 BG V , V Voltages ...............(INTV + 0.3V) to 0.3V REF RNG CC 6 11 I INTV ON CC I , V Voltages...................................... 2.7V to 0.3V TH FB GN PART 7 10 V V FB CC TG, BG, INTV , EXTV Peak Currents.................... 2A MARKING CC CC 8 9 V EXTV REF CC TG, BG, INTV , EXTV RMS Currents .............. 50mA CC CC 3717 GN PACKAGE Operating Ambient Temperature 16-LEAD PLASTIC SSOP Range (Note 4) ................................... 40 C to 85 C T = 125 C, q = 130 C/ W JMAX JA Junction Temperature (Note 2)............................ 125 C Storage Temperature Range ................. 65 C to 150 C Consult LTC Marketing for parts specified with wider operating temperature ranges. Lead Temperature (Soldering, 10 sec).................. 300 C 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 CC SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loop I Input DC Supply Current Q Normal 1000 2000 m A Shutdown Supply Current V = 0V 15 30 m A RUN/SS V Feedback Voltage Accuracy I = 1.2V (Note 3), V = 2.4V 0.65 0.65 % FB TH REF D V Feedback Voltage Line Regulation V = 4V to 36V, I = 1.2V (Note 3) 0.002 %/V FB(LINEREG) CC TH D V Feedback Voltage Load Regulation I = 0.5V to 1.9V (Note 3) l 0.05 0.3 % FB(LOADREG) TH g Error Amplifier Transconductance I = 1.2V (Note 3) 0.93 1.13 1.33 mS m(EA) TH t On-Time I = 30m A 186 233 280 ns ON ON I = 60m A 95 115 135 ns ON t Minimum On-Time I = 180m A 50 100 ns ON(MIN) ON t Minimum Off-Time I = 30m A 300 400 ns OFF(MIN) ON V Maximum Current Sense Threshold (Source) V = 1V, V = V 50mV l 108 135 162 mV SENSE(MAX) RNG FB REF/2 V V V = 0V, V = V 50mV l 76 95 114 mV PGND SW RNG FB REF/2 V = INTV , V = V 50mV l 148 185 222 mV RNG CC FB REF/2 V Minimum Current Sense Threshold (Sink) V = 1V, V = V + 50mV l 140 165 190 mV SENSE(MIN) RNG FB REF/2 V V V = 0V, V = V + 50mV l 97 115 133 mV PGND SW RNG FB REF/2 = INTV , V = V + 50mV l 200 235 270 mV V RNG CC FB REF/2 D V Output Overvoltage Fault Threshold 8 10 12 % FB(OV) D V Output Undervoltage Fault Threshold 25 % FB(UV) V RUN Pin Start Threshold l 0.8 1.5 2 V RUN/SS(ON) V RUN Pin Latchoff Enable Threshold RUN/SS Pin Rising 4 4.5 V RUN/SS(LE) V RUN Pin Latchoff Threshold RUN/SS Pin Falling 3.5 4.2 V RUN/SS(LT) I Soft-Start Charge Current 0.5 1.2 3 m A RUN/SS(C) I Soft-Start Discharge Current 0.8 1.8 3 m A RUN/SS(D) sn3717 3717fs 2 U WWW