LT3710 Secondary Side Synchronous Post Regulator FEATURES DESCRIPTIO n Generates a Regulated Auxiliary Output in Isolated The LT 3710 is a high efficiency step-down switching DC/DC Converters regulator intended for auxiliary outputs in single second- n 0.8V 1.5% Accurate Voltage Reference ary winding, multiple output power supplies. n Dual N-Channel MOSFET Synchronous Drivers The LT3710 drives dual synchronous N-channel MOSFETs n High Switching Frequency: Up to 500kHz and achieves high efficiency. With leading edge modula- n Programmable Current Limit Protection tion, it operates well with either primary side peak current n Programmable Soft-Start or voltage mode control. It is synchronized to the falling n Automatic Frequency Synchronization edge of the transformer secondary winding and can be n Small 16-Pin Thermally Enhanced TSSOP Package used in both single-ended and double-ended isolated power converter topologies. A high speed operational U amplifier is incorporated to achieve optimum compensa- APPLICATIO S tion and fast transient response. A user selectable discon- n 48V Isolated DC/DC Converters tinuous conduction mode improves light load efficiency. n Multiple Output Supplies The LT3710 is available in a thermally enhanced TSSOP-16 n Offline Converters exposed pad power package. , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO L1 V OUT1 3.3V AT 10A V V IN CC 36V BIAS TO 72V 10k V V BOOST CMDSH-3 DD CC V SYNC GBIAS COMP 10pF 4.7F CG LT3710 L2 Q1 V CSET TG FB C S 1.8H 0.006 V OUT2 680pF 0.1F FG 1.8V AT 10A SW + I SNS C Q2 B340A 4700pF ILCOMP BG OUT2 LTC1698 10k SS VA OUT 0.01F 3.3k BGS 180pF 3.01k 220 SYNC TG BG SG 33nF LT3781 PGND V FB + CL CL 2.32k 3710 F01 OPTODRV V REF V + GND C V FB C : POSCAP, 680F/4V PLEASE REFER TO FIGURE 3 OUT2 ISOLATION L2: SUMIDA CEP125-IR8MC-H IN THE APPLICATIONS SECTION BOUNDARY Q1, Q2: SILICONIX Si7440DP FOR THE COMPLETE SCHEMATIC Figure 1. Simplified Single Secondary Winding 3.3V and 1.8V Output Isolated DC/DC Converter 3710f 1 U ULT3710 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) TOP VIEW V Supply Voltage .................................................. 26V ORDER PART CC BOOST Pin Voltage With Respect to SW pin ........... 10V BOOST 1 16 GBIAS NUMBER TGATE 2 15 BGATE BOOST Pin Voltage With Respect to GND pin.......... 35V LT3710EFE SW 3 14 PGND SYNC Pin Voltage .................................................... 30V CSET 4 13 V CC Operating Junction Temperature Range 17 SYNC 5 12 CL (Notes 2, 3) ...................................... 40 C to 125 C + ILCOMP 6 11 CL Storage Temperature Range ................. 65 C to 150 C SS 7 10 VA OUT FE PART Lead Temperature (Soldering, 10 sec).................. 300 C V 8 9 BGS FB MARKING Note: If higher than 30V on SYNC pin is needed, add a 10k resistor in series with the pin. FE PACKAGE 3710EFE 16-LEAD PLASTIC TSSOP T = 125 C, q = 38 C/W JMAX JA EXPOSED PAD IS SGND (PIN 17) MUST BE CONNECTED TO PGND AND SOLDERED TO PCB 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 = 11V, operating maximum V = 24V, no load on any outputs A CC CC unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Overall Supply Voltage (V ) l824 V CC Supply Current (I ) VA 1.2V (Switching Off) 7 12 mA VCC OUT Boost Pin Current V = V + 8V, 0V V 24V BOOST SW SW TGATE High 2 3 mA TGATE Low 2 3 mA Voltage Amplifier VA Reference Voltage (V ) 0.788 0.8 0.812 V REF l 0.780 0.820 V FB Pin Input Current V = V 0.2 0.5 m A FB REF VA High 4.5 V OUT VA Low 0.8 V OUT VA Source Current l 100 300 m A OUT Open-Loop Gain 100 dB Gain Bandwidth Product 10 MHz Soft-Start Current 512 18 m A Current Limit Amplifier CA1 + Current Limit Threshold at (V V ) Common Mode Voltage from 0V to V 2.5V l 50 70 85 mV CL CL CC + BGATE Off Threshold at (V V ), BGS Pin Float Common Mode Voltage from 0V to V 2.5V 0 8 15 mV CL CL CC Switching Off Threshold at ILCOMP V 0.15 V ILCOMP + + Input Current (CL , CL)V = V 100 m A CL CL 3710f 2 U WWW