LTC1709-85 2-Phase, 5-Bit VID, Current Mode, High Efficiency, Synchronous Step-Down Switching Regulator FEATURES DESCRIPTIO n Output Stages Operate Antiphase Reducing Input The LTC 1709-85 is a 2-phase, VID programmable, syn- Capacitance Requirements and Power Supply chronous step-down switching regulator controller that Induced Noise drives two all N-channel external power MOSFET stages in n Dual Input Supply Capability for Load Sharing a fixed frequency architecture. The 2-phase controller n 5-Bit VID Code (VRM 8.5): V = 1.05V to 1.825V drives its two output stages out of phase at frequencies up OUT n True Remote Sensing Differential Amplifier to 300kHz to minimize the RMS ripple currents in both n Power Good Output Indicator input and output capacitors. The 2-phase technique effec- n 1% Output Voltage Accuracy tively multiplies the fundamental frequency by two, im- n Active Voltage Positioning Capable proving transient response while operating each channel n Current Mode Control Ensures Current Sharing at an optimum frequency for efficiency. Thermal design is n OPTI-LOOP Compensation Minimizes C also simplified. OUT n Three Operational Modes: PWM, Burst and Cycle Skip An operating mode select pin (FCB) can be used to select n Programmable Fixed Frequency: 150kHz to 300kHz among three modes including Burst Mode operation for n Wide V Range: 4V to 36V Operation IN highest efficiency. An internal differential amplifier provides n Adjustable Soft-Start Current Ramping true remote sensing of the regulated supplys positive and n Internal Current Foldback and Short-Circuit Shutdown negative output terminals as required in high current ap- n Overvoltage Soft Latch Eliminates Nuisance Trips plications. n Available in 36-Lead Narrow SSOP Package The RUN/SS pin provides soft-start and optional timed, U short-circuit shutdown. Current foldback limits MOSFET APPLICATIO S dissipation during short-circuit conditions when the overcurrent latchoff is disabled. OPTI-LOOP compensation n Server/Desktop Computers allows the transient response to be optimized for a wide n Internet Servers range of output capacitors and ESR values. n Large Memory Arrays , LTC and LT are registered trademarks of Linear Technology Corporation. n DC Power Distribution Systems OPTI-LOOP and Burst Mode are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO V IN 5V TO 28V + 10F 35V 0.1F V IN FCB TG1 4 0.002 RUN/SS BOOST1 0.47F 220pF SW1 1H 3.3k LTC1709-85 I BG1 TH SGND PGND + PGOOD SENSE1 SENSE1 5 VID BITS VID0VID4 TG2 0.002 V OUT EAIN BOOST2 0.47F 1.05V TO 1.825V 1H ATTENOUT SW2 40A ATTENIN BG2 V INTV DIFFOUT CC 10F C + OUT + V SENSE2 OS 1000F + 4V V SENSE2 OS 2 170985 F01 Figure 1. High Current Dual Phase Step-Down Converter 170985f 1 + S S U ULTC1709-85 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) TOP VIEW ORDER PART Input Supply Voltage (V ).........................36V to 0.3V IN NUMBER RUNN/SS 1 36 NC Topside Driver Voltages (BOOST1,2).........42V to 0.3V + SENSE1 2 35 TG1 Switch Voltage (SW1, 2) .............................36V to 5 V LTC1709EG-85 + + SENSE1 3 34 SW1 SENSE1 , SENSE2 , SENSE1 , EAIN 4 33 BOOST1 SENSE2 Voltages ................... (1.1)INTV to 0.3V CC PLLFLTR 5 32 V IN + EAIN, V , V , EXTV , INTV , RUN/SS, OS OS CC CC PLLIN 6 31 BG1 V , ATTENIN, ATTENOUT, PGOOD, BIAS FCB 7 30 EXTV CC VID25mVVID3 Voltages ........................7V to 0.3V I 8 29 INTV CC TH Boosted Driver Voltage (BOOST-SW) ..........7V to 0.3V SGND 9 28 PGND PLLFLTR, PLLIN, V , DIFFOUT V 10 27 BG2 DIFFOUT FCB Voltages ................................... INTV to 0.3V CC V 11 26 BOOST2 OS + I Voltage ................................................2.7V to 0.3V V 12 25 SW2 TH OS Peak Output Current <1m s(TGL1,2, BG1,2)................ 3A SENSE2 13 24 TG2 + SENSE2 14 23 PGOOD INTV RMS Output Current................................ 50mA CC ATTENOUT 15 22 V BIAS Operating Ambient Temperature Range ATTENIN 16 21 VID3 (Note 2) .............................................. 40 C to 85 C VID25mV 17 20 VID2 Junction Temperature (Note 3)............................. 125 C VID0 18 19 VID1 Storage Temperature Range ................. 65 C to 150 C G PACKAGE Lead Temperature (Soldering, 10 sec).................. 300 C 36-LEAD PLASTIC SSOP T = 125 C, q = 85 C/W JMAX JA Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V = 15V, V = 3.3V, V = 5V unless otherwise noted. A IN BIAS RUN/SS SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loop V Regulated Feedback Voltage I Voltage = 1.2V (Note 4) l 0.792 0.800 0.808 V EAIN TH V Maximum Current Sense Threshold l 62 75 88 mV SENSEMAX I Feedback Current (Note 4) 5 50 nA INEAIN V Output Voltage Load Regulation (Note 4) LOADREG Measured in Servo Loop, D I Voltage: 1.2V to 0.7V l 0.1 0.5 % TH Measured in Servo Loop, D I Voltage: 1.2V to 2V l 0.1 0.5 % TH V Reference Voltage Line Regulation V = 3.6V to 30V (Note 4) 0.002 0.02 %/V REFLNREG IN V Forced Continuous Threshold l 0.76 0.8 0.84 V FCB I Forced Continuous Current 0.17 1 m A FCB V Burst Inhibit (Constant Frequency) Measured at FCB pin 4.3 4.8 V BINHIBIT Threshold V Output Overvoltage Threshold Measured at V l 0.84 0.86 0.88 V OVL EAIN UVLO Undervoltage Lockout V Ramping Down 3 3.5 4 V IN g Transconductance Amplifier g I = 1.2V, Sink/Source 5m A (Note 4) 3 mmho m m TH g Transconductance Amplifier Gain I = 1.2V, (g Z No Ext Load) (Note 4) 1.5 V/mV mOL TH m L 170985f 2 U WWW