RL=Vin_UVP+IUVP_pull−up·RH− Vin_UVP+IUVP_pull−up·RH2−4·VUVPtℎ·IUVP_pull−up·RH

2·IUVP_pull−up

and Equation 8.a) for RM:

Equation 10

(10)

RM= VOVPtℎ−RL·IUVP_pull−up · RHVin_OVP−RL

The power consumption of the UVP-OVP network at given Vin is expressed as:

Equation 11

(11)

PUVP_OVP Vin = Vin2

RH+RM+RL

As an example, if Vin_UVP and Vin_OVP design values are 50 Vdc and 450 Vdc respectively, and RH is set to 6

Mohm: from Equations 9 and 10 we have RL = 43 kohm, and RM = 60 kohm respectively, while from Equation 11

the power consumption of the network at 230 Vac is about 17 mW.

4.15

Thermal shutdown

The power MOSFET junction temperature is sensed during the on-time through a diode integrated into the HV

section of the chip. If a junction temperature higher than the internal threshold TSD (160°C, typ.) is measured, the

PWM is disabled for tRESTART. In order to increase robustness against electromagnetic noises, the protection is

triggered only if the condition is met for nth = 3 consecutive switching cycles.

After tRESTART, the IC resumes switching with soft-start phase: if a junction temperature above TSD is still

measured for nth consecutive switching cycles, the protection is triggered and PWM is disabled again for

tRESTART; otherwise normal operation is restored.

During tRESTART, VCC is maintained between VCson and VCcon by the HV current source periodical activation.

Such a behavior is summarized in Figure 38. Thermal shutdown timing diagram.

Figure 38. Thermal shutdown timing diagram

VCCon

GD

t

VCC

VCSon

tRESTART

TJ

n < nth

TSD

tRESTART

t

t

n = nth

n = nth

VIPER31

General description

DS13285 - Rev 6

page 25/39