Application information

HVLED805

14/29

Doc ID 18077 Rev 1

Most of this current will charge the bypass capacitor connected between the Vcc pin and

ground and make its voltage rise linearly.

As the Vcc voltage reaches the start-up threshold (13 V typ.) the chip starts operating, the

internal power MOSFET is enabled to switch and the HV generator is cut off by the Vcc_OK

signal asserted high. The IC is powered by the energy stored in the Vcc capacitor.

threshold.

In this way, the self-supply circuit develops a voltage high enough to sustain the operation of

the device. This feature is useful especially during CC regulation, when the flyback voltage

At converter power-down the system will lose regulation as soon as the input voltage falls

voltage decay at system power-down.

Figure 11.

Timing diagram: normal power-up and power-down sequences

Vcc

DRAIN

t

tt

t

Vin

5.5 mA

t

t

Power-on

Power-off

Normal operation

CV mode

CC mode

Normal operation

Vcc

DRAIN

t

tt

t

Vin

5.5 mA

t

t

Power-on

Power-off

Normal operation

CV mode

CC mode

Normal operation