5.9.5

Inductor saturation detection (OCP2 function)

A second overcurrent level set at VCS_OCP2 (-0.75 V typ.) detects abnormal current values (e.g. due to boost

inductor saturation) and, on this occurrence for two consecutive switching cycles, activates a safety procedure

that immediately stops the converter activity until the current level reaches the zero-current threshold (VCS_ZCD).

The zero-current threshold monitor allows safe operations also during current surges occurring at power-up or

after a mains dip or missing cycle; in fact it allows switching start/restart only when the overcurrent event is

definitively over.

Figure 17. OCP2 timing

5.9.6

Feedback failure detection

The device handles the possible disconnection of both output voltage feedback and input current monitoring. At

startup, as soon as the VCC pin voltage reaches the VCC_ON turn-on threshold, the device checks the FB and CS

pins:

•

if the FB pin voltage is lower than the internal VFB_FF/EBM threshold (0.5 V typ.) a failure of the output

divider resistor is assumed (e.g. RFB_H resistor not mounted), then the device stops the switching activity

and reduces its consumption.

–

De-bounce time TFF/EBM_DB (1.8 µs typ.) is provided to avoid false triggering.

•

if the CS pin voltage is higher than the internal VCSD threshold (200 mV typ.) a failure of the current sensing

resistors is assumed (e.g. RTHD_CCM resistor not mounted and/or RS resistor burned), then the device

stops the switching activity and reduces its consumption. A recycle of VCC between the turn-off threshold

(VCC_OFF) and the turn-on threshold (V.) is needed to restart the converter.

–

De-bounce time TCSD_DB (10 µs typ.) is provided to avoid false triggering.

5.10

Line feedforward

To keep the maximum output power deliverable by the converter almost constant with respect to the AC input

voltage, a two-level discrete voltage feedforward is integrated in the controller. Basically, the AC input voltage

is monitored through the HV pin and internally compared with a fixed threshold to properly set the value of

equivalent multiplier gain KM (see Table 5. Electrical characteristics for details). The proper operation of the

converter, with the right KM multiplier gain, is guaranteed for an AC input voltage below 142 Vrms and above 166

Vrms.

L4985

Line feedforward

DS13769 - Rev 3

page 19/27