VIPER15 datasheet(33/40 Pages) STMICROELECTRONICS

33 / 40 page

VIPER15

Operation description

Doc ID 15455 Rev 5

33/40

Fixed the VINon and the VINoff levels, with reference to Figure 38, the following relationships

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

Equation 12

Equation 13

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, thus it is prone to

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

origin to 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 brown-out function is not used the BR pin has to be connected to GND, ensuring that

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

enable the brown-out function the BR pin voltage has to be higher than the maximum of

VDIS threshold (150 mV, see Table 8).

Figure 38.

Brown-out protection: BR external setting and timing diagram

Disable

DIS

in_OK

BRth

BRhyst

IN_DC

VDD

OUT

INon

INoff

DRAIN_START

in_OK

BRth

BRhyst

DDon

DDoff

DD(RESTART)

BRhyst

BRth

INoff

BRhyst

INoff

INon

BRhyst

−

BRhyst

INoff

INon

−

Obsolete

Product(s)

- Obsolete

Product(s)

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