TLC770X Datasheet, PDF (22/27 Pages) Texas Instruments – BiCMOS SUPPLY VOLTAGE SUPERVISORS

In order to ensure that a defined RESET signal is generated if there is a complete failure of the negative voltage, a
1 MΩ Pull-Down resistor is connected to the gate of the transistor, which makes sure that the transistor conducts in
 such a case, and that there is a Low level at the RESIN input of the device .
A Supply Voltage Supervisor can also be used in an audio amplifier, in order only to connect the loudspeaker via the
relay REL after a certain time delay (see Figure 20.).
Figure 20. Delay circuit in an audio amplifier
For cost reasons the positive and negative supply voltages which are used in such amplifiers are only controlled with
a single monitoring circuit. For simplicity, the negative supply voltage was chosen as the reference potential of the
circuit.
The supply voltage of the TLC7701 is divided down by a resistor R₁ and a zener diode D2 and stabilized at 5.1 V.
The desired threshold voltage V_t’ is set by the resistive voltage divider R₂ and R₃. This voltage divider must lie
between the negative and positive supply voltages, in order to indicate a failure of either supply.
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