TLC770X Datasheet, PDF (20/27 Pages) Texas Instruments – BiCMOS SUPPLY VOLTAGE SUPERVISORS

An additional possible application is the monitoring of several different supply voltages in a single system (Figure
18.).
Figure 18. Monitoring of a system with two different supply voltages
In this circuit, two different supply voltages of 3 V and 5 V are monitored. The system in which they are required is
brought into an active state only when both supply voltages have reached their nominal values.
 The delay time of the first device is of minor significance; it is required only to indicate a failure of the supply
ô ^{voltage which it is monitoring. For this reason, the capacitor Ct1 can be chosen with a comparatively low value (e.g.}
1 nF). When the 3 V supply voltage has reached its nominal value, the delay circuit of the second device begins
to operate. The delay time is determined by the capacitor C_t2, and should be chosen depending on the time taken to
switch on by the system.
In order to provide a defined RESET signal should one of the supply voltages fail, both devices are powered from
the same operating voltage. In such a case it makes sense to supply the monitoring circuits from the same voltage
source as the device to which the RESET signal is supplied.
It is also possible in this case to initiate a system RESET manually, by means of a switch at the RESIN input of the
TLC7703.
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