Secondary-Side Synchronous Rectifier Drive
Docket:LT8309 Secondary-Side Synchronous Rectifier Driver FeaTures n DescripTion
The LT®8309 is a secondary-side synchronous rectifier driver that replaces the output rectifier diode in a flyback topology. By replacing the diode with a N-channel MOSFET, applications are no longer restricted by the heat constraints of the output diode. The IC replicates the behavior of a diode by sensing the drain-to-source voltage to determine when the current becomes negative. The LT8309's low minimum on-and off-times help improve noise immunity. The fast propagation delay of 26ns allows applications to operate in discontinuous conduction mode (DCM) and critical conduction mode (CrCM). The gate driver features a 0.8 pull-down device for fast turn-offs. The 40V VCC rating allows the part to be driven from the output voltage or the rectified drain voltage of the MOSFET. A low 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. n Works with DCM and BCM/CrCM Conduction Mode Flyback Topologies VCC: 4.5V to 40V Supports Up to 150V MOSFETs 26ns Turn-Off Propagation Delay Accurate Minimum On and Off Timers for Reliable Operation Adjustable and Accurate Trip Point: +5mV to 30mV 1 Gate Driver Pull-Down SOT-23 5-Lead Package applicaTions High Output Current Flybacks High Efficiency Flybacks Typical applicaTion
40W, 5V Isolated Telecom Supply
VIN 36V TO 72V 5.33:1 10µF 15.4k 412k EN/UVLO VIN RFB RREF 60 100pF 147k 6.04k TC 30.9k 0.1µF SS VC 12.1k 15nF GATE SENSE GND INTVCC 4.7µF VOUT + 5V, 8A 100 95 90 EFFICIENCY (%) 85 80 75 70 VOUT
8309 TA01a Efficiency vs Load Current 10 1µF 2.2...
Moldel LineSeries: LT8309 (7)
LT8309ES5TRM, LT8309ES5 TRM