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ST1S50

Functional description

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Equation 12

To stabilize the loop and then to have the proper phase margin (> 45°) with the requested

5.3

Overcurrent protection

The ST1S50 device implements the pulse-by-pulse overcurrent protection. The peak

current is sensed through the high-side power MOSFET and when it exceeds the

overcurrent threshold the high-side is immediately turned off and the low-side conducts the

inductor current for the rest of the clock period.

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

by the overcurrent threshold, the output voltage drops out of regulation. If the FB falls below

0.734 V the switching frequency is divided by two to keep the inductor current limited around

The overload condition is allowed for 256 continuous clock cycles. In case the overload

condition persists for longer than 257 clock cycles, the HICCUP protection is triggered: the

device realizes a soft-start cycle and then, if the overcurrent protection is still triggered,

stops switching activities and remains disabled for the HICCUP times. Then it restarts with

a soft-start cycle.

Figure 6. Hiccup behavior with persistent short-circuit

Equation 13

If the feedback falls below 0.3 V before the 256 clock cycle, as a symptom of a short-circuit,

the HICCUP protection is triggered and the converter reacts as described above in this

section.



 G

 G





=

Soft-start duration

Hiccup duration



 2853934



=