7

The STPW12 detailed description

7.1

Power breaker intervention and thermal shutdown

The device disconnects the load if the power overcomes the pre-set threshold.

can be chosen with the help of the Figure 15. Power limit threshold vs. RS graph and can be rated for ¼ W.

precision resistors, the lower precision of the power limit.

The overcoming of the power limit threshold is signalled on the monitor/fault pin (see Figure 7. Masking time, fault

signal and Section 7.3 Monitor/fault pin description).

After a programmable delay time, the device attempts again to reconnect the load, by the auto-retry circuit. Each

auto-retry cycle starts with the defined masking time.

7.2

Current limit and thermal protections

The STPW12 is equipped with internal self-protections, such as: current limit and thermal shutdown.

Thermal shutdown is always active and occurs if the die temperature reaches the thermal shutdown threshold. If

this happens, the device switches off and the load is disconnected. The monitor/fault pin signal goes to low level

(power-off).

Once the die temperature decreases to the hysteresis value, the device automatically attempts to restart.

Current limit protection is always active and intervenes in case of strong overload or short-circuit on the output. In

such occurrence, the device internal power switch is immediately turned off and the load is disconnected.

Therefore the device immediately tries to activate the output. This on-off cycle is repeated until the overload is

removed or if thermal protection or power limit are activated.

During current limit events the monitor/fault pin is set to high logic level (4.5 V typ.).

7.3

Monitor/fault pin description

The monitor/fault pin provides two useful signals for the real-time control of the device and application status. A

monitor signal proportional to the power is continuously present on the pin. The relation between this signal and

the input power is almost linear and it is shown in Figure 6. Monitor signal vs. power and Figure 17. Monitor

voltage vs. power.

The target accuracy of monitor signal in relation to the input power is +/-15%, in the typical operating condition

Therefore the signal goes to low logic level, the output is turned off and the auto-retry cycle starts.

The same happens if the power limit overcomes during the PWM masking time. See the following pictures and

Table 5. Monitor signal truth table for more details.

STPW12

The STPW12 detailed description

DS12478 - Rev 1

page 11/23