TLC770X Datasheet, PDF (23/27 Pages) Texas Instruments – BiCMOS SUPPLY VOLTAGE SUPERVISORS

The time delay is set by means of the capacitor C_t = 220 µF to about 5 s. The output RESET is connected to the
gate of the transistor Q. As long as the RESET output is Low, the transistor Q will remain non conducting, and no
current will flow through the relay REL. After the elapse of the delay time t_d, the RESET signal becomes High, and
the transistor Q conducts and energizes the relay REL.
The output circuit is protected with a clamp diode, in order to eliminate safely the energy stored in the coil of the
relay REL when the transistor is switched off.
5.2 Applications in Systems
An additional potential application of the TLC770X is in battery backed memory systems (Figure 21.).
Figure 21. Voltage monitoring in a battery backed memory system
The operation of the system with the full supply voltage and after the elapse of the delay time t_d can be described as
follows.
The microcomputer controls the input CONTROL of the TLC7705, by means of the signal CSH1. Whenever the
microcontroller makes access to the memory, the output CSH1 becomes Low, and it selects the memory ( CS = Low)
via the path CONTROL-RESET of the TLC7705 (see Figure 5.).
Should there be a failure of the supply voltage, the memory must be isolated from the microcontroller, so than there
can be no uncontrolled write and read accesses to the memory. Therefore, whenever the supply voltage falls below
the permissible nominal value, the memory is put into an inactive state ( CS = High) by means of the output RESET.
To ensure that in such a case there will be no loss of data in the memory, the latter, together with the monitoring
circuit, are supplied by the battery should there be a failure of the supply voltage. In this situation the very low
current consumption of the TLC7705 is an advantage, since this results in a very long life for the battery. The
CONTROL input is switched off in this state, so that undefined levels at the microcontroller output CSH1 will not
result in an increase of the current consumption (see Section 3).
5.3 Application Hints
When using the TLC770X, the following precautions must be taken in order to ensure that a RESET circuit operates
absolutely correctly.
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