VIPER318HDTR datasheet(20/40 Pages) STMICROELECTRONICS

20 / 40 page

Figure 30. Connection for input undervoltage protection/disable (isolated or non-isolated topologies)

GND

DRAIN

GND

VCC

UVP

COMP

CONTROL

VIPER31

DIN

~ AC

OVP

CIN

from VAUX or VOUT

If UVP function is not required, the UVP pin must be left floating. In this case, noise immunity of the pin is

guaranteed by the internal pull-up IUVP_pull-up (1 uA, typ.) present in the UVP block.

If UVP function is required, RH value can be set arbitrarily, but some Mohms at least are recommended in order to

minimize the power consumption of the UVP network. Then, if Vin_UVP is the desired input undervoltage threshold,

the value of RL can be found from the following formula:

Equation 2

(2)

RL=

VUVP_th

Vin_UVP−VUVP_th

RH +IUVP_pull−up

Equation 3

(3)

PUVPVin = Vin2RH+RL

Thanks to the ultra-low consumption, the UVP pin can be used as an input to disable the SMPS from external,

reaching the lowest input power consumption while the SMPS is still connected to the AC mains but not delivering

power to its output.

The purpose of the UVP debounce time tUVP_DEB is also to guarantee some hold-up in case of a missing cycle of

the input line, as illustrated in Figure 31. Hold-up in case of input line missing cycles.

VIPER31

Undervoltage protection

DS13285 - Rev 3

page 20/40

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