5.9.2

AC brownout (BO function)

During the normal operation, in order to protect the PFC pre-regulator from excessive RMS current, if the AC line

voltage falls below the VHVPK_BO brownout threshold (around 71 Vac) for at least 630 ms typ. (see TDB_ACBO

parameter in Table 5. Electrical characteristics), the switching activity is stopped.

5.9.3

Output overvoltage (OVP function)

To limit an output voltage overshoot, e.g. due to a heavy load release or at startup with light-load, the device stops

the switching activity as soon as the instantaneous output voltage VOUT is higher than 7% typ. in respect to the

programmed value.

In fact, the device detects an overvoltage condition monitoring the FB pin which is proportional to the

instantaneous value of the output voltage VOUT and in steady-state conditions sits at the internal reference of

the error amplifier (VREF = 2.5 V).

As soon as the FB voltage exceeds the steady-state value by 7% (VFB > VFB_S), the switching activity is stopped

until it gets back close to it (VFB < VFB_R).

De-bounce time TDOVP_DB (50 µs typ.) is provided to avoid false activation of the protection.

During the OVP condition, to avoid undesired IC shutdown, as soon as the VCC pin voltage falls below the

VCC_HVSTUP_OVP threshold (11.5 V typ.) the internal HV-startup is turned on to bring VCC voltage to the turn-on

threshold VCC_ON.

Figure 16. OVP timing

5.9.4

Overcurrent (OCP1 function)

To limit the peak inductor current in case of extra request (e.g. heavy load changes), the device implements a

cycle-by-cycle overcurrent protection. The device monitors the CS pin during the power switch on-time and as

soon as the voltage on the CS pin goes below VCS_OCP1 (-0.49 V typ.), the internal overcurrent comparator is

triggered and terminates the conduction cycle of the power switch before the normal PWM circuit does. In this

way, the peak inductor current is limited to a maximum of 0.49/RS.

L4985

Protections

DS13769 - Rev 3

page 18/27