Datasheet SRK1001 (STMicroelectronics) - 3

SRK1001 Block diagram and pin connection N. Name Function
Supply voltage of the device. A bypass capacitor to GND, located as close to IC pins as possible, helps obtain a 4 VCC clean supply voltage for the internal control circuitry and acts as an effective energy buffer for the pulsed gate drive current. Drain voltage sensing. This pin must be connected to the drain terminal of the synchronous rectifier MOSFET 5 DVS through a series resistor of at least 300 Ω. Auxiliary supply voltage of the device. When VCC voltage is lower than UVLO voltage threshold (VCC_SO_On), the bypass capacitor on the VCC pin (coupled to application VOUT through a diode) is supplied by the VAUX pin 6 VAUX if this is connected to an auxiliary winding or to an external capacitor sourced by a DVS voltage rectifier. If the functionality is not used, VAUX pin must be connected to VCC pin. Programming pin for blanking time after turn-off. A resistor connected from this pin to GND, supplied by an 7 TOFF internal current source, sets a voltage VTOFF; depending on this voltage level, the user can choose the blanking time after turn-off suitable for application requirements. Programming pin for blanking time after turn-on. A resistor connected from this pin to GND, supplied by an internal current source, sets a voltage VTON; depending on this voltage level, the user can choose the blanking time after turn-on, suitable to mask ZCD comparator output and avoid premature turn-off due to parasitic voltage 8 TON oscillation on DVS pin. In tracking with VTON, the thresholds to enter/exit automatic sleep mode are derived. A capacitor larger than 60 pF (100 pF typ.) between this pin and GND sets the internal timer mode for SR MOSFET turn-off in mixed CCM/DCM operation. If no capacitor is used, timer mode is set for turn-off in QR or DCM operation. No capacitor is also required when SYNC signal is used for turn-off.
DS13155
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Rev 1 page 3/27
Document Outline 1 Block diagram and pin connection 2 Maximum ratings 3 Typical application schematic 4 Electrical characteristics 5 Operation description 5.1 Drain voltage sensing 5.2 Turn-on 5.3 Minimum TON programming 5.4 Adaptive turn-off and TIMER 5.4.1 Fixed frequency mixed DCM/CCM operation 5.4.2 QR operation (with valley skipping) 5.4.3 Fixed frequency DCM operation 5.4.4 Variable frequency CCM operation 5.5 Minimum TOFF programming 5.6 Start-up phase 5.7 Low consumption mode operation: sleep-mode, burst mode, disable state 5.8 DIS/SYNC pin functions 5.9 VAUX pin operation in CC regulation 5.9.1 Example for parameter calculations 5.10 Operation in CC regulation and short circuit 5.11 Adaptive gate drive 6 Layout guidelines 7 Package mechanical data Revision history