When input voltage surpasses the programmed value, the input overvoltage protection stops the switching activity

and activates the discharge current IBLEED (where required).

During iOVP, 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.

IBLEED current discharges the input capacitor to speed up the recover from surge occurrence.

In case of steady input overvoltage, the VCC pin rises until the IBLEED generator automatically reduces the

absorbed current. At this occurrence, the HVSU unit provides the whole current for HVLED101 and the input

capacitor is discharged by a current that is almost equal to ICC plus the internal consumption of the HVSU unit.

When HVSU voltage is lower than protection level, the HVSU charges VCC to reach VCC-ON (if required) and

active mode is entered.

Figure 16. iOVP waveforms

VCC

ViOVP

VHVSU

Low consumption

(fault)

Active Mode

Temporary Overvoltage

(e.g. surge)

Active Mode

VCC-ON

IHVSU

IVcc

IBLEED

IHV-ON

ICC-L - ICHG-L

ICC

~19V

~ ICC

VCC-OFF

6.8.3

Brownout protection (BO)

In order to avoid operation at insufficient input voltage, the IC moves to low consumption mode if the input voltage

is lower than the programmed threshold (Table 9) for at least TBO (500 ms min.). During masking time (TBO-LEB),

activated after brownout triggering time, the HVSU comparator is ignored to prevent false restart due to EMI filter

resonance oscillations, while IBLEED is turned on to discharge any residual oscillation due to EMI filter operating

condition at turn-off instant.

After the end of TBO_LEB, the input voltage is checked to be higher than the threshold only during the charging

period of VCC: a small time (TDBNC) is applied after HVSU activation to prevent false reading. To be noted that the

value of the resistance that is in series with the HVSU pin, multiplied by ICHG-H, sets the hysteresis for brownout

threshold voltage.

HVLED101

Protections

DS14143 - Rev 2

page 25/36