VIPER37 datasheet(30/35 Pages) STMICROELECTRONICS

30 / 35 page

Operation description

VIPER37

30/35

Doc ID 022218 Rev 1

When the VINon and the VINoff levels are fixed, with reference to Figure 33, the following

relationships can be established for the calculation of the resistors RH and RL:

Equation 9

Equation 10

For a proper operation of this function, VIN on must be less than the peak voltage at

minimum mains and VIN off less than the minimum voltage on the input bulk capacitor at

minimum mains and maximum load.

The BR pin is a high impedance input connected to high value resistors, it is therefore prone

to pick up noise, which might alter the OFF threshold when the converter operates or

creates an undesired switch-off of the device during ESD tests.

It is possible to bypass the pin to ground with a small film capacitor (e.g. 1-10 nF) to prevent

any malfunctioning of this kind.

If the brownout function is not used, the BR pin must be connected to GND, ensuring that

the voltage is lower than the minimum VDIS threshold (50 mV), see Table 8.

Figure 33.

Brownout protection: BR external setting and timing diagram

BRhyst

BRth

INoff

BRhyst

INoff

INon

BRhyst

−

BRhyst

INoff

INon

−

VIPER37 数据表(PDF) 30 Page - STMicroelectronics