General description

VIPer11

22/37

DS11873 Rev 5

5.11

Overload protection

To manage the overload condition, the IC embeds the following main blocks: the OCP

comparator to turn off the power MOSFET when the drain current reaches its limit (IDLIM) ,

the up and down OCP counter to define the turn-off delay time in case of continuous

overload (tOVL = 50 ms typ.) and the timer to define the restart time after protection tripping

(tRESTART = 1 s typ.).

In case of short-circuit or overload, the control level on the inverting input of the PWM

comparator is greater than the reference level fed into the inverting input of the OCP

comparator. As a result, the cycle-by-cycle turn-off of the power switch is triggered by the

OCP comparator instead of PWM comparator. Every cycle where this condition is met, the

OCP counter is incremented. If the fault condition lasts longer than tOVL (corresponding to

the counter end-of-count), the protection is tripped, the PWM is disabled for tRESTART, then it

resumes switching with soft-start and, if the fault is still present, it is disabled again after

tOVL. If the converter is definitively operated at FOSC_MIN, (see Section 5.7: Pulse-skipping),

the IC is turned off after the time tOVL_MAX (100 ms or 200 ms or 400 ms typ., depending on

FOSC) and then automatically restarted with soft-start phase, after tRESTART.

The OLP management prevents IC from operating indefinitely at IDLIM and the low repetition

rate of the restart attempts of the converter avoids IC overheating in case of repeated fault

events.

After the fault removal, the IC resumes working normally. If the fault is removed earlier than

the protection tripping (before tOVL), the tOVL-counter is decremented on a cycle-by-cycle

basis down to zero and the protection is not tripped. If the fault is removed during tRESTART,

the IC waits for the tRESTART period has elapsed before resuming switching.

In fault condition the VCC ranges between VCSon and VCCon levels, due to the periodical

activation of the HV current source recharging the VCC capacitor.

Figure 30. Short-circuit condition