DS12978 Rev 1

17/28

VIPer26K

General description

28

4.9

Burst mode

When the voltage VCOMP drops below the threshold, VCOMPL, the power MOSFET is kept in

the OFF state and the consumption is reduced to IDD0 current. As a reaction at the energy

delivery stop, the VCOMP voltage increases and as soon as it exceeds the threshold VCOMPL

+ VCOMPL_HYS, the converter starts switching again with consumption level equal to IDD1

current. This ON-OFF operation mode, referred to as “burst mode” and reported in Figure 4,

reduces the average frequency, which can go down even to a few hundred hertz, thus

minimizing all frequency-related losses and making it easier to comply with energy saving

regulations. During burst mode, the drain current limit is reduced to the value IDLIM_bm in

order to avoid the audible noise issue.

Figure 23. Load-dependent operating modes: timing diagram

4.10

Automatic auto restart after overload or short-circuit

The overload protection is implemented in an automatic way using the integrated up-down

counter. Every cycle, it is incremented or decremented depending on whether the current

logic detects the limit condition or not. The limit condition is the peak drain current, IDLIM.

After the reset of the counter, if the peak drain current is continuously equal to the level IDlim,

the counter will be incremented till the fixed time, tOVL, after that the power MOSFET switch

ON is disabled. It is activated again, through the soft-start, after the tRESTART time.

In the case of overload or a short-circuit event, the power MOSFET switching is stopped

after a time that depends from the counter and that can be as maximum equal to tOVL. The

protection occurs in the same way until the overload condition is removed.

This protection ensures restart attempts of the converter with low repetition rate, so that it

works safely with extremely low power throughput and avoiding the IC overheating in case

of repeated overload events.

If the overload is removed before the protection tripping, the counter is decremented cycle-

by-cycle down to zero and the IC is not stopped.