VIPER17HN datasheet(25/31 Pages) STMICROELECTRONICS

25 / 31 page

VIPER17

Operation descriptions

25/31

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 VBRth,0.45 V typ value, 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 VDD

voltage continuously oscillates between the VDDon and the UVLO thresholds, as shown in

the timing diagram of Figure 31 on page 26. 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 31.

The Brown-out comparator is provided also with a current hysteresis, IBRhyst.With this

approach is possible to set the VINon threshold and VINoff thresholds separately, by properly

choosing the resistors of the divider connect to the BR pin.

I DS

VFBBM

50 mV

hyster.

Burst-mode

Normal-mode

50 mV

hyster.

Burst-mode

Normal-mode

100

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