VIPER37HE datasheet(29/35 Pages) STMICROELECTRONICS

29 / 35 page

VIPER37

Operation description

Doc ID 022218 Rev 1

29/35

Figure 32.

Burst mode timing diagram, light load management

8.12

Brownout protection

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

undervoltage is detected.

The brownout comparator is internally referenced to VBRth,Table 8, 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 brownout condition is present, the VDD voltage

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

diagram of

Figure 33. 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

previously mentioned voltage hysteresis, see

Figure 5.

The brownout comparator is provided also with a current hysteresis, IBRhyst. The user must

set the rectified input voltage above which the Power MOSFET starts switching after

brownout event, VINon, and the rectified input voltage below which the Power MOSFET is

switched off, VINoff. Thanks to the IBRhyst, see Table 8, these two thresholds can be set

separately.

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