LTC3765/LTC3766 Isolated Forward Converter DIRECT FLUX LIMIT GUARANTEES NO TRANSFORMER SATURATION ACTIVE CLAMP RESET 8μH +VIN 4T 2.2μF 100V ×3 0.1μF 200V –VIN 61.9k t +VOUT 4T 4mΩ 1W μF 4.7μF VCC NDRV PG – IS RUN IS+ IS– IS+ AG SSFLT RCORE 33nF GND 13.3k PGND 0.1μF DELAY IN– FS/UV 8.25k 22k SG SW VCC MODE NDRV VS+ 1.82k t t PT+ RUN VIN LTC3766 1μFF 1nF 11.5k PT – 2.5:2 2.2nF 250VAC VS– VAUX FG IN+ LTC3765 1.87k 470pF pF 115nF ISMAG 4.99k 9k –VOUT 10μF 16V 100Ω 0.75Ω VCC 68μF 16V ×2 1.82k 100Ω VCC + 22μF 16V ×2 1.82k 75Ω 1μF 200V 6mΩ 1W 100k t SS 1k FB GND PGND IPK FS/SYNC SGD FGD ITH 604Ω 4.12k 2k 33nF 56.2k 60.4k 15k 47pF 2.2pF (Actual Schematic) Improved Forward Converter Technology The LTC®3765 and LTC3766 chipset combine to form an advanced feature set, low component count, isolated synchronous forward converter. Direct Flux Limit™ technology prevents transformer saturation under all conditions. Active clamp transformer reset increases efficiency and reduces the solution size. Secondary-side control ensures reliable control of the output voltage and current while providing the fastest transient response. Accurate and Adjustable Current Limit LTC3765/LTC3766 Features/Benefits n n n n n n n n n n n Direct Flux Limit Feature Synchronous Rectification Active Clamp Transformer Reset Secondary-Side Control Fast and Accurate Average Current Limit Self-Starting Architecture Multiphase Capable (Up to 250W/Phase) True Remote Output Voltage Sense No Opto-Coupler Required Very Fast Transient Response Clean Start-Up into a Prebiased Load Overtemperature/OVP Protection OUTPUT VOLTAGE (V) n OUTPUT CURRENT (A) L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Direct Flux Limit is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. LTC3765/LTC3766 Demo Board 1/8th Brick (0.9” × 2.3” × 0.47”) Top View Bottom View (Actual Size) (Actual Size) This circuit demonstrates a high level of performance, efficiency and small solution size attainable using these parts in an activeclamp-reset isolated forward converter power supply. It produces a regulated 12V, 12.5A output from an input voltage range of 18V to 72V, making it well suited for telecom, datacom and industrial applications. Demo Board Performance Curves 12V/12.5A Output p from 18V to 72V Input 95 14 12 10 93 8 6 92 POWER DISSIPATION (W) EFFICIENCY ( %) 94 4 Eff, 24VIN Eff, 48VIN PD, 24VIN PD, 48VIN 91 90 2 4 6 8 10 12 2 0 IOUT (A) Efficiency and Power Loss Curves Output Ripple, 20MHz BW Transient Response Waveforms IOUT 5A/DIV 50mV/DIV VOUT 500mV/DIV 2μs/DIV CONDITIONS: 48VIN, 12V at 11AOUT 50μs/DIV CONDITIONS: 48VIN, 6A to 12A STEP LOAD www.linear.com/3765 n 1-800-4-LINEAR 0612