L6563H datasheet(35/48 Pages) STMICROELECTRONICS

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L6563H

Application information

Doc ID 16047 Rev 2

35/48

6.8

High-voltage start-up generator

Figure 51

shows the internal schematic of the high-voltage start-up generator (HV

generator). It is made up of a high-voltage N-channel FET, whose gate is biased by a 15 M

resistor, with a temperature-compensated current generator connected to its source.

Figure 51.

High-voltage start-up generator: internal schematic

The HV generator is physically located on a separate chip, made with BCD off-line

technology able to withstand 700 V, controlled by a low-voltage chip, where all of the control

functions reside.

With reference to the timing diagram of Figure 52, when power is first applied to the

converter the voltage on the bulk capacitor (Vin) builds up and, at about 80 V, the HV

generator is enabled to operate (HV_EN is pulled high) so that it draws about 1 mA. This

current, minus the device's consumption, charges the bypass capacitor connected from pin

Vcc (16) to ground and makes its voltage rise almost linearly.

L6563H Datasheet(PDF) 35 Page - STMicroelectronics