48V No-Opto Isolated Applications VOUT+ 12V 2A 4:1 VIN 22V TO 75V 10µF 412k EN/UVLO 60.8µH VIN RFB 15.4k 3.8µH 243k 100µF VOUT– RREF 6.04k LT3748 GATE TC SENSE SS VC 56.2k 2nF GND 10k INTVCC 0.033Ω 4.7µF 4700pF The Transformer is the Only Part Crossing the Isolation Barrier The LT®3748 is a high input voltage isolated flyback DC/DC controller that does not require an opto-isolator, third winding or signal transformer for feedback. The output voltage is sensed from the primary-side flyback signal, and is set with two external resistors and the transformer turns ratio. The LT3748 operates over a 5V to 100V input voltage range, drives an external N-channel power MOSFET and maintains better than ±5% overall regulation. Output Load and Line Regulation Features Input Voltage Range: 5V to 100V 12.6 No Opto-Coupler Required Primary-Side Winding VOUT Sensing 12.4 n n n VOUT Set with Two External Resistors 1.9A Onboard Gate Driver Boundary Mode Operation Off-the-Shelf Transformers Only One Part Crossing the Isolation Barrier MSOP-16 with High Voltage Spacing Programmable Soft-Start n n n n 12.2 VOUT (V) n 12.0 11.8 n n VIN = 72V VIN = 48V VIN = 36V 11.6 11.4 0 L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. 0.5 1.0 1.5 LOAD CURRENT (A) 2.0 LT3748 Demo Board LT3748 Package Outline TOP VIEW VIN 1 16 RFB EN/UVLO 3 INTVCC GATE SENSE GND 14 RREF 5 6 7 8 12 11 10 9 1mm TC VC SS GND MS PACKAGE 16 (12)-LEAD PLASTIC MSOP Primary-Side Switch Node Waveform ACTUAL CIRCUIT SIZE: 38mm × 19mm × 9.5mm N-TRANSFORMER TURNS RATIO The LT3748 is available in an MSOP-16 package with 4 pins removed for high voltage spacing. The high level of integration, readily available off-the-shelf transformers and the use of boundary mode operation results in a simple, clean application solution. VC NVOUT VIN tSP OUTPUT VOLTAGE SENSING AT SWITCH NODE Examples of Off-the-Shelf Transformers (See Data Sheet for More Options) Target Application 20V to 75V → 12V/1A 20V to 75V → 5V/2A 10V to 40V → 10V/2.5A 30V to 75V → 12V/1A 30V to 75V → 5V/3A 10V to 40V → 5V/3A 20V to 75V → 12V/2.5A Supplier Size (W × L × H) (mm) Part Number Pulse Pulse Pulse Wurth Wurth Wurth Wurth 18 × 14 × 13 18 × 14 × 13 29 × 22 × 11.5 18 × 14 × 13 18 × 14 × 13 18 × 14 × 13 29 × 23 × 11.5 PA2367NL PA1260NL PA3177NL 750311424 750311423 750311564 750311607 Other Related Flyback Converters and Controllers from Linear Technology Part Number LT3511 LT3512 LT3574 LT3573 LT3575 LT3758 LT3757 VIN Range (V) 4.5 to 100 4.5 to 100 3 to 40 3 to 40 3 to 40 5.5 to 100 2.9 to 40 No Opto-Coupler Required Onboard Switch Max Output Power √ √ √ √ √ 0.24A/150V 0.40A/150V 0.65A/60V 1.25A/60V 2.5A/60V NA NA 2.5W 5W 3W 7W 14W 60W 60W www.linear.com/3748 n 1-800-4-LINEAR 1110