L99VR01STR datasheet(23/47 Pages) STMICROELECTRONICS

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Figure 38. Watchdog timing diagram

VCW

RST

Vwhth

Vwlth

Iw_off

Iw_on

Twol

Twop

Since the RST output pin is shared between the watchdog circuit and the output voltage monitoring circuit, for

applications where the watchdog is not needed, to prevent the watchdog from generating RST pulses without

anyhow losing the reset functionality of the Vo monitoring, the Vcw pin has to be connected to Vo. Vcw pin must be

always tied to ground by an external capacitor (Ctw) when the watchdog is used.

Note:

when the watchdog timer is used and the regulator recovers from a thermal shut-down event or recovers from

an output under-voltage event (including the recovery from output under-voltage event at the regulator output

turning on), the reset pin might be pulled back high with a delay longer than Trd, in the range between Trd

and Trd +Twol due to the watchdog that might affect the RST pin release. The watchdog will not affect the

RST pin release in the case where recovering from a thermal shut-down event or recovering from an output

under-voltage event (including the recovery from output under-voltage event at the regulator output turning on)

the Io drops below Iw_off before Trd. The output current Io consists in the load current, the current drawn from the

RST pin and the TW pin through the pull-down resistors connected to Vo when the RST and the TW pins are

asserted low and the current needed to charge/discharge the output capacitor Co.

Note:

when the watchdog timer is used, in case of an output under-voltage event not making Vo drop to zero volt,

since the watchdog will still be running during the output under-voltage condition, the first watchdog timeout

after the reset pin is released coming out of the output under-voltage event might occur before expected

(0≤Timeout≤Twop-Twol).

Table 13. Watchdog timer

Usage of watchdog timer

Connection of Vcw Pin

Watchdog timer is not used

Connect to the Vo pin

Watchdog timer is used

Connect to an external capacitor Ctw

4.7

Thermal warning and thermal shutdown

To warn the microcontroller about a severe temperature increase, a thermal warning output has been

implemented (L99VR01J version only). If the device detects a junction temperature above Twarn, the advanced

thermal warning (TW) output pin is pulled low while the voltage regulator and its features remain all active. The

TW pin will return to its high logic level (equal to the Vo output value) once the temperature falls below the

threshold Twarn - Twarn_hyst.

L99VR01

Thermal warning and thermal shutdown

DS13649 - Rev 3

page 23/47

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