TLC770X Datasheet, PDF (15/27 Pages) Texas Instruments – BiCMOS SUPPLY VOLTAGE SUPERVISORS

1.5
1.3
1.1
0.9
0.7
VCC - Vt
0.5
0.3
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
minimum pulswidth at SENSE-input [µs]
Figure 12. Dependence of the minimum pulse width at the SENSE input on the reduction of the supply
voltage (V_DD=5V)
Below the minimum pulse width of 1.6 µs, no further reaction of the circuit can be expected. In order to determine the
minimum pulse width, a pulse was applied to the SENSE input (see Figure 13.) whose amplitude ∆V was varied. The
minimum pulse width t_p gives the value at which the circuit no longer shows any reaction for specific amplitude ∆V.
Figure 13. The signal at the SENSE input for determining the minimum pulse width t_p
In certain applications a slower reaction of the voltage monitoring circuit may be required than that which is provided
by the integrated circuit itself. In this case, a low pass filter can be inserted before the SENSE input which will filter
out voltage reductions of short duration. The resistance of this RC network must not however be chosen with too
high a value, in order not excessively to influence the integrated voltage divider at the SENSE input. Since this
integrated voltage divider has a resistance of several 100 kΩ, resistors at the input of about 1000 Ω can be used,
without significantly influencing the threshold voltage.
A factor which influences briefly the reaction of the circuit is the presence of very fast rise times of the supply voltage
(rise time < 20 µs). These can cause parts of the circuit of the TLC770X to be over driven for short periods. In view
of the high internal resistance of the circuit, it takes a certain time before the desired operating points have again
been reached. The result of this is a delay of the charging process of the capacitor of about t _v ≈ 1 ms (see Figure
14.).
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