L99VR01 datasheet(24/47 Pages) STMICROELECTRONICS

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Figure 39. Thermal warning diagram

When junction temperature reaches the Tprot_j/s thermal shutdown threshold the regulator output is quickly shut-

off through the internal Fast Output Discharge circuit; to be reactivated, junction temperature has to decrease

below Tprot_j/s- Tprot_hyst. Being TW an open-drain output an external resistance (RTW) is needed between the TW

pin and the Vo pin. The external resistance value can be in a range between 4.7 KΩ and 20 KΩ. Be aware that

the current flowing through the TW pin drawn from Vo when the TW pin is pulled low may affect the watchdog

activation/deactivation based on the regulator output current consumption monitoring. Leave floating if not used.

4.8

Overvoltage detection by advanced thermal warning read-out

The TW pin also provides diagnostics about output overvoltage (OV); to distinguish between a thermal warning

event and an output overvoltage event, two different signals are generated at the same TW output pin. How

reported in the previous paragraph a thermal warning event detection sets the TW pin LOW, instead an output

overvoltage event generates a square wave at the TW pin (Figure 40. Square wave on TW pin generated during

an overvoltage). Overvoltage detection has higher priority than thermal warning detection so that concurrence of

thermal warning and over voltage events leads to a square wave like in the case of overvoltage detection (as

shown in Figure 41. Warning signal caused by overvoltage and thermal warning on TW pin).

Figure 40. Square wave on TW pin generated during an overvoltage

Tw_per

A typical example of thermal warning and overvoltage failures management is depicted in Figure 41. Warning

signal caused by overvoltage and thermal warning on TW pin.

L99VR01

Overvoltage detection by advanced thermal warning read-out

DS13649 - Rev 3

page 24/47

L99VR01 Datasheet(PDF) 24 Page - STMicroelectronics