DocID023654 Rev 2

13/27

ST1S41

Functional description

Figure 6. Module and phase bode plot

5.3

Overcurrent protection

The ST1S41 implements the pulse-by-pulse overcurrent protection. The peak current is

sensed through the high-side power MOSFET and when it exceeds the first overcurrent

threshold (OCP1) the high-side is immediately turned off and the low-side conducts the

inductor current for the rest of the clock period and the following high-side cycle is disabled.

This implements a division by two of the switching frequency in case of overload to keep the

output current limited below the current limit value.

During overload condition, since the duty cycle is not set by the control loop but is limited by

the overcurrent threshold, the output voltage drops out of regulation. If the feedback falls

below 0.3 V, the switching frequency is reduced to one fourth and the current limit threshold

is folded back to around 2 A. Thanks to the current and frequency foldback the stress on the

device and on the external power components is reduced in case of severe overload or

dead-short to ground of the output.