LTC3778 Wide Operating Range, TM No R Step-Down Controller SENSE FEATURES DESCRIPTIO n Wide V Range: 4V to 36V The LTC 3778 is a synchronous step-down switching IN n Sense Resistor Optional regulator controller for computer memory, automobile n True Current Mode Control and other DC/DC power supplies. The controller uses a n 2% to 90% Duty Cycle at 200kHz valley current control architecture to deliver very low duty n t 100ns cycles without requiring a sense resistor. Operating fre- ON(MIN) n Stable with Ceramic C quency is selected by an external resistor and is compen- OUT n Dual N-Channel MOSFET Synchronous Drive sated for variations in V and V . IN OUT n Power Good Output Voltage Monitor Discontinuous mode operation provides high efficiency n 1% 0.6V Reference operation at light loads. A forced continuous control pin n Adjustable Current Limit reduces noise and RF interference, and can assist second- n Adjustable Switching Frequency ary winding regulation when the main output is lightly n Programmable Soft-Start + loaded. SENSE and SENSE pins provide true Kelvin n Output Overvoltage Protection sensing across the optional sense resistor or the n Optional Short-Circuit Shutdown Timer sychronous MOSFET. n Micropower Shutdown: I 30m A Q n Fault protection is provided by internal foldback current Available in a 1mm 20-Lead TSSOP Package limiting, an output overvoltage comparator, optional short- U circuit shutdown timer and input undervoltage lockout. APPLICATIO S Soft-start capability for supply sequencing is accom- n Notebook and Palmtop Computers, PDAs plished using an external timing capacitor. The regulator n Battery Chargers current limit level is user programmable. Wide supply n Distributed Power Systems range allows operation from 4V to 36V at the input and n DDR Memory Power Supply from 0.6V up to (0.9)V at the output. IN n Automobile DC Power Supply , LTC and LT are registered trademarks of Linear Technology Corporation. No R is a trademark of Linear Technology Corporation. SENSE TYPICAL APPLICATIO R ON 1.4M I ON Efficiency vs Load Current C SS V IN 0.1F V IN 100 5V TO 28V C IN M1 RUN/SS TG 10F V = 5V Si4884 L1 IN 35V C C 1.8H SW V 3 OUT 500pF 90 2.5V C 0.22F B I BOOST C 10A TH OUT + V = 25V D IN B 180F R C LTC3778 CMDSH-3 4V 20k SGND INTV 2 80 CC M2 D1 DRV CC Si4874 B340A BG + SENSE + 70 R2 C VCC 40.2k 4.7F SENSE PGOOD PGND 60 0.01 1 10 0.1 V FB R1 LOAD CURRENT (A) 12.7k 3778 F01b 3778 F01a Figure 1. High Efficiency Step-Down Converter 3778f 1 EFFICIENCY (%) U ULTC3778 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART TOP VIEW Input Supply Voltage (V , I )..................36V to 0.3V IN ON NUMBER Boosted Topside Driver Supply Voltage RUN/SS 1 20 BOOST (BOOST) ................................................... 42V to 0.3V V 2 19 TG ON LTC3778EF + PGOOD 3 SENSE , SW Voltage.................................... 36V to 5V 18 SW + V 4 17 SENSE DRV , EXTV , (BOOST SW), FCB, RNG CC CC I 5 16 SENSE TH RUN/SS, PGOOD Voltages .................... 7V to 0.3V FCB 6 15 PGND V V Voltages................... INTV + 0.3V to 0.3V ON, RNG CC SGND 7 14 BG I , V Voltages...................................... 2.7V to 0.3V TH FB I 8 13 DRV ON CC TG, BG, INTV Peak Currents.................................. 2A CC V 9 12 INTV FB CC TG, BG, INTV RMS Currents ............................ 50mA CC EXTV 10 11 V CC IN Operating Ambient Temperature F PACKAGE Range (Note 4) ................................... 40 C to 85 C 20-LEAD PLASTIC TSSOP Junction Temperature (Note 2)............................ 125 C T = 125 C, q = 110 C/ W JMAX JA 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 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 3) l 0.594 0.600 0.606 V FB TH D V Feedback Voltage Line Regulation V = 4V to 30V, I = 1.2V (Note 3) 0.002 %/V FB(LINEREG) IN TH D V Feedback Voltage Load Regulation I = 0.5V to 1.9V (Note 3) 0.05 0.3 % FB(LOADREG) TH I Feedback Pin Input Current 5 100 nA FB g Error Amplifier Transconductance I = 1.2V (Note 3) l 1.4 1.7 2 mS m(EA) TH V Forced Continuous Threshold l 0.57 0.6 0.63 V FCB I Forced Continuous Pin Current V = 0.6V 1 2 m A FCB FCB t On-Time I = 60m A, V = 1.5V 200 250 300 ns ON ON ON I = 60m A, V = 0V 110 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 = 0.56V l 113 133 153 mV SENSE(MAX) RNG FB + V V V = 0V, V = 0.56V l 79 93 107 mV SENSE SENSE RNG FB V = INTV , V = 0.56V l 158 186 214 mV RNG CC FB V Minimum Current Sense Threshold V = 1V, V = 0.64V 67 mV SENSE(MIN) RNG FB + V V V = 0V, V = 0.64V 47 mV SENSE SENSE RNG FB V = INTV , V = 0.64V 93 mV RNG CC FB D V Output Overvoltage Fault Threshold 7.5 10 12.5 % FB(OV) D V Output Undervoltage Fault Threshold 340 400 460 mV FB(UV) 3778f 2 U WWW