VIPER317LDTR datasheet(15/39 Pages) STMICROELECTRONICS

15 / 39 page

At nominal input voltage (230 VAC), typical and worst-case consumptions are 2.4 mW and 3.0 mW respectively

(corresponding to RG_typ = 45 Mohm and RG_min = 36 Mohm). This means that, with a careful design, the

overall no-load input power consumption of the application can be maintained very low (typically, below 10 mW

@230 VAC)

Power-off: when the IC is disconnected from the mains, or there is a mains interruption, for some time the

converter keeps on working, powered by the energy stored in the input bulk capacitor. When it is discharged

below a critical value, the converter is no longer able to keep the output voltage regulated. During the power

down, when the DRAIN voltage becomes too low, the HV current source remains off and the IC is stopped as

soon as VCC drops below the UVLO threshold, VCcoff.

Figure 25. Power ON and power OFF

VIN_DC

Power-off:

VIN decreases

VDRAIN

Power-on:

HV current source enabled

VCCon

ICH1

ICH2

VCSon

VCCoff

HV current source is no

more activated because

of too low VDRAIN

UVLO

VCC

HV current source is

disabled here

VOUT

Output regulation is lost here

VHV_START

Power-on

Power-off

Steady-state

4.5

Soft startup

The internal soft-start function of the VIPER31 progressively increases the cycle-by-cycle current limitation set

point from zero up to IDLIM.

The soft-start time, tSS, which is internally set at 8 ms, is activated at any attempt of converter power-on and at

any restart after a fault event.

The feature is used to reduce the stress of the power components and increase the reliability of the system.

VIPER31

General description

DS13285 - Rev 6

page 15/39

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