ST1S12 description

AN2728

6/20

1.2

Current limit and short-circuit protection

In overcurrent protection mode, when the peak current reaches the current limit, the device

In case of heavy short-circuit when the feedback voltage is lower than 0.1 V (typ.), the loop

compared with 0.4 V (typ.) to clamp the upper limit of the inductor current. In this condition

the maximum output limitation current is reduced to 300 mA instead of 1 A. At the same time

the DMD circuit clamps the lower boundary of the inductor current. One RS flip-flop is being

used to control the PMOS and NMOS switches. When the feedback voltage is higher than

0.1 V (typ.) voltage, the device returns to normal closed-loop switching operation (Figure 6).

Figure 6.

Short-circuit protection simplified schematic

Q

R

S

DMD

COM

0.1V

COM

V

IN

V

OUT

C2

+

-

-

+

R1

R2

L1

V

V

FB

GND

GND

V

REF1

V

C

GND

Q

R

S

DMD

COM

0.1V

COM

V

IN

V

OUT

C2

+

-

-

+

R1

R2

L1

V

V

FB

GND

GND

V

REF1

V

C

GND