SRK1001 Datasheet Adaptive synchronous rectification controller for flyback converter SO8 package Features Secondary side synchronous rectification controller optimized for flyback converter Suitable for QR and mixed CCM/DCM fixed frequency operation Wide V operating voltage range 3.7 to 32 V CC CC regulation operation down to 2V output supported Very low quiescent current in low consumption mode (170 A) High-voltage sensing input for SR MOSFET drain-source voltage (185 V AMR) Operating frequency up to 300 kHz High-current gate-drive output for N-MOSFET Fast turn-on with minimum delay time and adaptive turn-off logic Programmable minimum T and T ON OFF Low consumption mode entry by DIS pin, by primary side burst-mode detection or by detection of SR MOSFET conduction lower than programmed min. T ON SO8 package Applications AC-DC adapters Battery chargers / quick chargers USB power delivery (profile 4) Industrial SMPS Product status link SRK1001 Description Product summary The SRK1001 controller is designed for secondary side synchronous rectification (SR) in flyback converters, suitable for operation in QR and mixed CCM/DCM fixed Order code SRK1001 frequency circuits. Package SO8 It provides a high-current gate-drive output capable of driving N-channel Power Packing Tape and reel MOSFETs. The control scheme of this IC is such that the SR MOSFET is switched on as soon as current starts flowing through its body diode, and then switched off as current approaches zero. The fast turn-on with minimum delay and innovative adaptive turn-off logic allow maximizing the conduction time of the SR MOSFET and eliminating the effect of parasitic inductance in the circuit. The device enters low consumption mode when it detects primary controller burst- mode operation, or when the DIS pin is pulled up by the user, or when the SR MOSFET conduction falls below the programmed minimum T . This improves the ON converter efficiency at light load, where synchronous rectification is no longer beneficial. After the converter restarts switching or the DIS pin goes low again and the IC detects that the current conduction in the rectifiers has increased 20% above the min T programmed value, the IC exits low consumption mode and resumes switching ON operation. DS13155 - Rev 1 - November 2019 www.st.com For further information contact your local STMicroelectronics sales office.SRK1001 Block diagram and pin connection 1 Block diagram and pin connection Figure 1. Internal block diagram COMPARATORS HV CLAMP TIMER DVS ON ZCD DIS/SYNC TON ADAPTIVE CONTROL TOFF CONTROL LOGIC VAUX DRIVER POWER GD MANAGEMENT & SWITCH OVER VCC GND Figure 2. Pin connections (top view) DIS/SYNC 1 8 TON GD 2 7 TOFF GND 3 6 VAUX VCC 4 5 DVS SO8 Table 1. Pin functions N. Name Function This pin has two functions: disable and synchronization input. Asynchronous turn-off of SR MOSFET always occurs after DIS pin voltage shows a positive rising edge and the synchronous rectification stays disabled as long as it remains at the high level. If the DIS pin voltage stays high for at least 4 switching cycles, the device enters low consumption mode. DIS/ 1 SYNC Synchronization function requires that no external capacitor must be mounted between TON pin and GND, so that SR MOSFET turn-off is accomplished by the positive rising edge of the applied SYNC signal or when triggered by ZCD comparator output. This pin is pulled high by internal current source (5 A) if not used, it must be grounded. Gate driver output. Totem pole output stage is able to drive power MOSFET with high peak current levels. To 2 GD avoid excessive gate voltages in case the device is supplied with a high VCC, the high level voltage of this pin is clamped to about 11.5 V. The pin must be connected directly to the SR MOSFET gate terminal. Return of the device bias current and return of the gate drive current. Route this pin close to the source terminal 3 GND of synchronous rectifier MOSFET. DS13155 - Rev 1 page 2/27