8.3.2 User-Programmable Reset Time Delay

The reset time delay can be set to a minimum value of 80 µs by leaving the CT pin floating, or a maximum value

of approximately 6.2 seconds by connecting 10 µF delay capacitor. The reset time delay (tD) can be

programmed by connecting a capacitor no larger than 10 µF between CT pin and GND.

The relationship between external capacitor (CCT) in µF at CT pin and the time delay (tD) in seconds is given by

Equation 2.

tD = -ln (0.29) x RCT x CCT + tD (CT pin = Open)

(2)

Equation 2 is simplified to Equation 3 by plugging RCT and tD (CT pin = Open) given in Section 7.5 section:

tD = 618937 x CCT + 80µs

(3)

Equation 4 solves for external capacitor value (CCT) in units of µF where tD is in units of seconds

CCT = (tD- 80µs) ÷ 618937

(4)

The recommended maximum delay capacitor for the TLV840 is limited to 10 µF as this ensures there is enough

time for the capacitor to fully discharge when the reset condition occurs. When a voltage fault occurs, the

previously charged up capacitor discharges, and if the monitored voltage returns from the fault condition before

the delay capacitor discharges completely, the reset delay will be shorter than expected because the delay

capacitor will begin charging from a voltage above zero. Larger delay capacitors can be used so long as the

capacitor has enough time to fully discharge during the duration of the voltage fault. The amount of time required

to discharge the delay capacitor relative to the reset delay increases as VDD overdrive increases as shown in

Figure 8-3.

VDD Fault Underoltage (V)

0.6

0.8

1

1.2

1.4

1.6

1.8

2

5

10

15

20

25

30

35

40

45

50

55

CTR_

25°C

Figure 8-3. CCT Discharge Time During Fault Condition (VIT- = 2.1 V, CCT = 1 µF)

TLV840

SNVSBC3C – DECEMBER 2019 – REVISED SEPTEMBER 2020

www.ti.com

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