AN728 Datasheet | Vishay

features include: D programmable start/stop D less than 5-m A supply current in UVLO mode D internal start-up circuit, programmable soft-start, and power_good output. The following sections discuss in detail design considerations for creating an efficient 800-m W flyback converter with the Si9113. Refer to the application circuit from Figure 6. Start/Stop Programming The European Telemunication Standards Institute (ETSI) requires the NT1 and the regenerator directed towards the line terminal to remain at a high impedance state for as long as the input line voltage stays below 18 V. The high impedance state Input Current Input Voltage Into +VIN at +VIN A 1.4 m V is defined by the maximum leakage current through the equipment and its minimum input capacitance. In this state the leakage current must be less than 10 m A and the capacitance more than 1 m F. The Si9113 includes a very high input impedance-window parator, which can be programmed to set an accurate undervoltage lockout (UVLO) level with adequate hysteresis. The programmable hysteresis avoids unintentional locking of the system during start up, especially when the system is fed from long loops of telephone line. The parators need a mere 0.05-m A input bias current. Moreover, when in UVLO mode, the Si9113 disables the internal reference generator, soft-start, oscillator circuit, and most of the control section to reduce the supply current below 5 m A. This keeps the total current drawn by the converter below 10 m A and meets the ETSI standard. See Figure 1 for the current behavior of the Si9113 with respect to the input voltage. When the converter is on, the VCC is supplied by the boot-strap winding and the internal depletion MOSFET opens. Figure 2 shows how the hysteresis is achieved. Refer to equations 1 and 2 to calculate the resistor values for proper undervoltage lockout and the hysteresis. V START + R3 ) R4 ) R5 R5 V STOP + R3 ) R5 R5 8.8 8.8 (1) (2) 23.5 18.0 100 m 10 m Hi Z Shutdown Operating Hi Z Shutdown...