During brownout, the internal THD optimizer drives the internal switched resistor always OFF (setting δc = 0 in

Section 6.3.1 ) and the THD pin is set in high impedance.

Figure 17. Brownout protection

VBO

VCC-SHD

VCC

Low Consumption

VHVSU

Active Mode

Active Mode

VCC-ON

< TBO

TBO

TBO-LEB

IHVSU

IBLEED

IHV-ON

BO exit

Ignored

TDBNC

VCC-OFF

TDBNC

Complete restart by ramp-up

6.8.4

Undervoltage protection (UVP)

Primary side regulation sample and hold constantly monitors the output voltage. If it steadily falls below the VUVP

threshold for at least TUVP, the IC is shut down and ART state is invoked to try a new operating attempt. Note

that, during the VCC recycling, the ART timer is frozen during VCC recharging phase (from turn-off to turn-on

thresholds); furthermore, as TART elapses, the HV current generator is activated immediately, without waiting that

the VCC turn-off threshold is reached. At operation resuming attempt after ART state, the IC starts from the

ramp-up phase.

6.8.5

General fault pin and NTC connection

The HVLED101 embeds one general purpose pin intended to disable the switching activity and move the IC into

low consumption if the voltage at this pin falls below a threshold level or is left floating. Also in this case (like for

UVP), as the protection is triggered, the ART state is invoked: after TART elapses, the IC waits for the FAULT

condition reset before resuming operation (starting from ramp-up phase).

The FAULT pin is mainly used to manage an NTC thermistor: in fact, the lower threshold has a well-defined

hysteresis, the pin sources a precise current to create the desired thermal hysteresis for final application.

HVLED101

Protections

DS14143 - Rev 2

page 26/36