Datasheet

Operation descriptions VIPER17

24/32 DocID14419 Rev 9

Figure 30. Burst mode timing diagram, light load management

7.12 Brown-out protection

Brown-out protection is a not-latched shutdown function activated when a condition of mains

under voltage is detected. The Brown-out comparator is internally referenced to V

BRth

threshold, see Table 8 on page 7, and disables the PWM if the voltage applied at the BR pin

is below this internal reference. Under this condition the power MOSFET is turned off. Until

the Brown out condition is present, the V

voltage continuously oscillates between the

DDon

and the UVLO thresholds, as shown in the timing diagram of Figure 31 on page 25. A

voltage hysteresis is present to improve the noise immunity.

The switching operation is restarted as the voltage on the pin is above the reference plus

the before said voltage hysteresis. See Figure 5 on page 9.

The Brown-out comparator is provided also with a current hysteresis, I

BRhyst

. The designer

has to set the rectified input voltage above which the power MOSFET starts switching after

brown out event, V

INon

, and the rectified input voltage below which the power MOSFET is

switched off, V

INoff

. Thanks to the I

BRhyst

, see Table 8 on page 7, these two thresholds can

be set separately.

DRAIN

FBbm

50 mV

hyster.

Burst-mode

Normal - mode

50 mV

hyster.

Burst-mode Burst-mode

Normal - mode Normal - mode

100