AN2753 datasheet(23/31 Pages) STMICROELECTRONICS

23 / 31 page

AN2753

Precision of the regulation and output voltage ripple

Doc ID 14654 Rev 2

23/31

3.7

Brownout protection

The brownout protection is basically an unlatched device shutdown functionality whose

typical use is to sense a mains undervoltage. The VIPer17 has a pin (BR, pin 5) dedicated to

this function that must be connected to the DC HV bus. If the protection is not required, it

can be disabled by connecting the pin to ground. In the presented converter the brownout

protection is implemented but can be disabled by changing the jumper J3 (see Figure 2)

settings. The settings of the jumper J3 are shown in Figure 28 and 29. The converter's

shutdown is accomplished by means of an internal comparator internally referenced to 450

mV (typ, VBRth) that disables the PWM if the voltage applied at BR pin is below the internal

reference, as shown in Figure 30. PWM operation is re-enabled as the BR pin voltage is

more than 450 mV plus 50 mV of voltage hysteresis that ensures noise immunity. The

brownout comparator is also provided with current hysteresis. An internal 10 µA current

generator is ON as long as the voltage applied at the brownout pin is below 450 mV and is

OFF if the voltage exceeds 450 mv plus the voltage hysteresis.

Figure 26.

OVP protection

Figure 27.

OVP protection (detail)

AN2753 Datasheet(PDF) 23 Page - STMicroelectronics