TPS37 datasheet(22/48 Pages) TI

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8.3.5 User-Programmable Sense Delay

TPS37 has adjustable sense release time delay with external capacitors. Channel timing are independent of

each other. Sense delay is used as a de-glitcher or ignoring known transients.

• A capacitor in CTS1 program the excursion detection on SENSE1.

• A capacitor in CTS2 program the excursion detection on SENSE2.

• No capacitor on these pins gives the fastest detection time indicated in the Section 7.6.

8.3.5.1 Sense Time Delay Configuration

The time delay (tCTS) can be programmed by connecting a capacitor between CTS1 pin and GND, CTS2 for

channel 2. In this section CTSx represent either channel 1 or channel 2.R

The relationship between external capacitor CCTSx_EXT (typ) and the time delay tCTSx (typ) is given by Equation 4.

tCTSx (typ) = -In (0.28) x RCTSx (typ) x CCTSx_EXT (typ) + tCTSx (no cap)

(4)

RCTSx = is in kilo ohms (kOhms)

CCTSX_EXT = is given in microfarads (μF)

tCTSx = is the sense time delay (ms)

The sense delay varies according to three variables: the external capacitor (CCTSx_EXT), CTS pin internal

resistance (RCTSx) provided in Section 7.5, and a constant. The minimum and maximum variance due to the

constant is show in Equation 5 and Equation 6:

tCTSx (min) = -ln (0.31) x RCTSx (min) x CCTSx_EXT (min) + tCTSx (no cap (min))

(5)

tCTRx (max) = -ln (0.25) x RCTSx (max) x CCTSx_EXT (max) + tCTSx (no cap (max))

(6)

The recommended maximum sense delay capacitor for the TPS37 is limited to 10 μF as this ensures enough

time for the capacitor to fully discharge when a voltage fault occurs. Also, having a too large of a capacitor value

can cause very slow charge up (rise times) and system noise can cause the the internal circuit to trip earlier or

later near the threshold. This leads to variation in time delay where it can make the delay accuracy worse in the

presence of system noise.

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 delay will be shorter than

expected. The capacitor will begin charging from a voltage above zero and resulting in shorter than expected

time delay. A larger delay capacitor can be used so long as the capacitor has enough time between fault events

to fully discharge during the duration of the voltage fault. To ensure the capacitor is fully discharged, the time

period or time duration between fault events needs to be greater than 10% of the programmed sense time delay.

TPS37

SNVSBJ1D – OCTOBER 2020 – REVISED DECEMBER 2021

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