LTC1775 High Power TM No R Current Mode SENSE Synchronous Step-Down Switching Regulator FEATURES DESCRIPTIO n The LTC 1775 is a synchronous step-down switching Highest Efficiency Current Mode Controller n regulator controller that drives external N-channel power No Sense Resistor Required n MOSFETs using few external components. Current mode 300mV Maximum Current Sense Voltage n control with MOSFET V sensing eliminates the need for Stable High Current Operation DS n a sense resistor and improves efficiency. Largely similar Dual N-Channel MOSFET Synchronous Drive n to the LTC1625, the LTC1775 has twice the maximum Wide V Range: 4V to 36V IN n sense voltage for high current applications. The frequency Wide V Range: 1.19V to V OUT IN n of a nominal 150kHz internal oscillator can be synchro- 1% 1.19V Reference n nized to an external clock over a 1.5:1 frequency range. Programmable Fixed Frequency with Injection Lock n Very Low Drop Out Operation: 99% Duty Cycle TM Burst Mode operation at low load currents reduces n Forced Continuous Mode Control Pin switching losses and low dropout operation extends oper- n Optional Programmable Soft Start ating time in battery-powered systems. A forced continu- n Pin Selectable Output Voltage ous mode control pin can assist secondary winding n Foldback Current Limit regulation by disabling Burst Mode operation when the n Output Overvoltage Protection main output is lightly loaded. n Logic Controlled Micropower Shutdown: I < 30m A Q Fault protection is provided by foldback current limiting n Available in 16-Lead Narrow SSOP and SO Packages and an output overvoltage comparator. An external ca- U pacitor attached to the RUN/SS pin provides soft start APPLICATIO S capability for supply sequencing. A wide supply range n Notebook Computers allows operation from 4V (4.3V for LTC1775I) to 36V at the n Automotive Electronics input and 1.19V to V at the output. IN n Battery Chargers , LTC and LT are registered trademarks of Linear Technology Corporation. n No R and Burst Mode are trademarks of Linear Technology Corporation. SENSE Distributed Power Systems TYPICAL APPLICATION Efficiency vs Load Current 100 LTC1775 V IN V = 10V IN SYNC V 5V TO IN V = 5V f = 150kHz OUT C IN 28V C 0.1m F + 95 FCB = INTV SS TK CC 22m F M1 30V RUN/SS TG SUD50N03-10 L1 4 90 V = 3.3V OUT 6m H V OUT V SW PROG C 0.33m F 3.3V B BOOST + C 10A 85 D1 OUT R C D B 680m F MBRS340 10k CMDSH-3 6.3V I INTV TH CC C 80 C 2.2nF M2 SGND BG SUD50N03-10 + 75 C VCC 4.7m F V PGND OSENSE 70 1775 F01 0.01 0.1 1 10 LOAD CURRENT (A) Figure 1. High Efficiency Step-Down Converter 1775 F01b 1 EFFICIENCY (%) U ULTC1775 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART Input Supply Voltage (V , TK) ................. 36V to 0.3V IN TOP VIEW NUMBER Boosted Supply Voltage (BOOST)............. 42V to 0.3V EXTV 1 16 V CC IN Boosted Driver Voltage (BOOST SW) ...... 7V to 0.3V SYNC 2 15 TK LTC1775CGN Switch Voltage (SW) ....................................36V to 5V RUN/SS 3 14 SW LTC1775CS EXTV Voltage ...........................................7V to 0.3V FCB 4 13 TG CC LTC1775IGN I Voltage ................................................2.7V to 0.3V I 5 12 BOOST LTC1775IS TH TH FCB, RUN/SS, SYNC Voltages .....................7V to 0.3V SGND 6 11 INTV CC V 7 10 V , V Voltages ........(INTV + 0.3V) to 0.3V BG OSENSE OSENSE PROG CC GN PART MARKING V 8 9 PGND Peak Driver Output Current < 10m s (TG, BG) ............ 2A PROG 1775 INTV Output Current ........................................ 50mA GN PACKAGE S PACKAGE CC 16-LEAD NARROW 16-LEAD PLASTIC SO 1775I Operating Ambient Temperature Range PLASTIC SSOP LTC1775C .............................................. 0 C to 70 C T = 125 C, q = 130 C/W (GN) JMAX JA T = 125 C, q = 110 C/W (S) JMAX JA LTC1775I (Note 5).............................. 40 C to 85 C Junction Temperature (Note 2)............................. 125 C Consult factory for Military grade parts. Storage Temperature Range ................ 65 C to 150 C Lead Temperature (Soldering, 10 sec)................. 300 C ELECTRICAL CHARACTERISTICS The l denotes specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V = 15V unless otherwise noted. A IN SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loop I V Feedback Current V Pin Open, I = 1.19V (Note 3) 10 50 nA IN OSENSE PROG TH V Regulated Output Voltage I = 1.19V (Note 3) OUT TH 1.19V (Adjustable) Selected V Pin Open l 1.178 1.190 1.202 V PROG 3.3V Selected V = 0V l 3.220 3.300 3.380 V PROG 5V Selected V = INTV l 4.900 5.000 5.100 V PROG CC V Reference Voltage Line Regulation V = 4V to 20V, I = 1.19V (Note 3), 0.001 0.01 %/V LINEREG IN TH V Pin Open PROG V Output Voltage Load Regulation I = 2V (Note 3) l 0.020 0.2 % LOADREG TH I = 0.5V (Note 3) l 0.035 0.2 % TH V Forced Continuous Threshold V Ramping Negative l 1.16 1.19 1.22 V FCB FCB I Forced Continuous Bias Current V = 1.19V 1 2 m A FCB FCB V Output Overvoltage Lockout V Pin Open 1.24 1.28 1.32 V OVL PROG I V Input Current PROG PROG 3.3V V V = 0V 3.5 7 m A OUT PROG 5V V V = 5V 3.5 7 m A OUT PROG I Input DC Supply Current Q Normal Mode EXTV = 5V (Note 4) 500 m A CC Shutdown V = 0V, 4V < V < 15V 15 30 m A RUN/SS IN V RUN/SS Pin Threshold l 0.8 1.4 2 V RUN/SS I Soft Start Current Source V = 0V 1.2 2.5 4 m A RUN/SS RUN/SS D V Maximum Current Sense Threshold V = 1V, V Pin Open 260 300 340 mV SENSE(MAX) OSENSE PROG 2 U WWW