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STCH02 Datasheet(PDF) 6 Page - STMicroelectronics |
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STCH02 Datasheet(HTML) 6 Page - STMicroelectronics |
6 / 24 page Device description and block diagram STCH02 6/24 DocID028766 Rev 1 3FB Control input for duty cycle control. A voltage set 65 mV below the threshold VFBB activates the burst mode operation. A level close to the threshold VFBL means that we are approaching the cycle-by-cycle overcurrent setpoint. 4ZCD Transformer's demagnetization sensing for the quasi resonant operation and input/output voltage monitor. A negative-going edge triggers the MOSFET's turn-on. The current sourced by the pin during MOSFET's ON-time is monitored to get an image of the input voltage to the converter, in order to compensate the internal delay of the current sensing circuit and achieve a CC regulation independent of the mains voltage. Still, the pin voltage is sampled-and-held right at the end of transformer's demagnetization to get an accurate image of the output voltage to be used for overvoltage protection (OVP). Please note that the maximum IZCD sunk/sourced current has to not exceed ± 3 mA (AMR) in the entire input voltage range. No capacitor is allowed between the pin and the auxiliary winding of the transformer. 5 SENSE Input to the PWM comparators. The current flowing in the MOSFET is sensed through a resistor connected between the pin and GND. The resulting voltage is compared with an internal reference (0.75 V max.) to determine the MOSFET's turn- off. The pin is equipped with 380 ns blanking time after the gate drive output goes high for improved noise immunity. If a second comparison level located at 1 V is exceeded the IC is stopped and restarted after VDD has dropped below VDDR (4.5 V typ.). 6GND Circuit ground reference and current return for both - the signal part of the IC and the gate drive. All of the ground connections of the bias components should be tied to the trace going to this pin and kept separate from any pulsed current return. 7 GD A gate driver with a totem pole output stage for the external power MOSFET. 8VDD Supply voltage of the device. An electrolytic capacitor, connected between this pin and ground, is initially charged by the internal high voltage start-up generator. When the device is running the same generator will keep it charged in case the voltage supplied by the auxiliary winding is not sufficient. This feature is disabled in case a protection is tripped. Sometimes a small bypass capacitor (0.1 µF typ.) connected between the pin and GND might be useful to get a clean bias voltage for the signal part of the IC. Table 4. Pin functions (continued) No. Name Function |
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