LT8309 Secondary-Side Synchronous Rectifier Driver FeaTuresDescripTion n Works with DCM and BCM/CrCM Conduction Mode The LT®8309 is a secondary-side synchronous rectifier Flyback Topologies driver that replaces the output rectifier diode in a flyback n VCC: 4.5V to 40V topology. By replacing the diode with a N-channel MOSFET, n Supports Up to 150V MOSFETs applications are no longer restricted by the heat constraints n 26ns Turn-Off Propagation Delay of the output diode. The IC replicates the behavior of a n Accurate Minimum On and Off Timers for Reliable diode by sensing the drain-to-source voltage to determine Operation when the current becomes negative. The LT8309's low n Adjustable and Accurate Trip Point: +5mV to –30mV minimum on- and off-times help improve noise immunity. n 1Ω Gate Driver Pull-Down The fast propagation delay of 26ns allows applications to n SOT-23 5-Lead Package operate in discontinuous conduction mode (DCM) and critical conduction mode (CrCM). The gate driver features applicaTions a 0.8Ω pull-down device for fast turn-offs. The 40V VCC n rating allows the part to be driven from the output volt- High Output Current Flybacks n age or the rectified drain voltage of the MOSFET. A low High Efficiency Flybacks quiescent current of 400µA maximizes efficiency at low output currents. 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. Typical applicaTion40W, 5V Isolated Telecom SupplyEfficiency vs Load Current 5.33:1 V 100 IN VOUT+ 36V TO 10µF 412k • 5V, 8A 72V 60Ω 400µF 95 EN/UVLO VIN 100pF • 10Ω LT8309 VIN = 48V WITH LT8309 15.4k VCC 90 LT3748 147k R 1µF FB 85 RREF 6.2V 6.04k 2.2k VIN = 48V WITH PDS760 DIODE DRAIN 80 INTVCC EFFICIENCY (%) TC GATE GATE 75 GND SS SENSE 30.9k V 70 C GND INTVCC 4.7µF 12mΩ 12.1k VOUT– 0.1µF 65 4.7µF 8309 TA01a 0 1 2 3 4 5 6 7 8 15nF LOAD CURRENT (A) 8309 TA01b 8309fa For more information www.linear.com/LT8309 1
