6.4

Output voltage clamp

This internal protection circuit clamps the output voltage to a maximum safe value, typically 15 V, if the input

voltage exceeds the VCLAMP threshold. In this condition, the device regulates the output voltage, therefore the

power dissipation increases. Thermal shutdown can occur if the overvoltage persists.

6.5

Current limiting

During the operation, if the load current reaches the ILIM threshold, an overload is detected. The current limiting

circuit reduces the conductivity of the power MOSFET, in order to clamp the output current at the ISHORT

value. The overload threshold and current limit can be customized by the limiting resistor RLim Figure 3. Typical

application circuit.

As shown in Section 1 Diagram, the device uses an internal N-channel sense FET with a fixed ratio, to monitor

the output current and limit it at the level set by the user.

To achieve the requested current limitation, the RLim value can be selected by using the following table, together

with the graph in Figure 8. ILim and IShort vs. RLim - (STEF12SGR) and Figure 9. ILim and IShort vs. RLim -

(STEF12SPUR). Higher resistor values can be used, but due to the current limit trend shown in the before

mentioned graphs, the minimum values of ILIM and ISHORT are asymptotically limited.

Table 7. ILIM / ISHORT vs. RLim STEF12SGR

RLim (Ω)

15.4

22

24.9

30

39

49.9

100

200

300

ILIM (A)

8

5.5

5.1

4.4

3.8

3.2

2.4

1.7

1.5

ISHORT (A)

5.1

2.8

2.6

2.3

1.9

1.5

0.8

0.4

0.3

Table 8. ILIM / ISHORT vs. RLim STEF12SPUR

RLim (Ω)

15.4

22

24.9

30

39

49.9

100

200

300

ILIM (A)

5.9

4.6

4.4

3.8

3.2

2.8

2

1.5

1.3

ISHORT (A)

3.2

2.4

2.2

1.9

1.7

1.5

0.8

0.4

0.3

Note:

Missing or shorted RLim causes current limit circuit malfunction and may lead to the device damage.

6.6

Thermal shutdown

If the device temperature exceeds the thermal shutdown threshold (TSHDN), typically 165 °C, the power MOSFET

is turned off and the load disconnected.

On the STEF12S latch version, the EN/Fault pin of the device is automatically set to an intermediate voltage

(typically 1.3 V), in order to signal the overtemperature event to the system controller.

The device can be reset from this condition either by cycling the supply voltage or by pulling down the EN pin

below the Vil threshold and then releasing it.

On the autoretry version (STEF12SA), the EN/Fault pin is set to a low logic level and the autoretry circuit attempts

to restart the device with soft-start once the die temperature is reduced to 145 °C typ. (165 °C minus the

hysteresis value, 20 °C typ.).

STEF12S

Output voltage clamp

DS13002 - Rev 5

page 9/31