ZHCSMU6E august 2020 – august 2023 TPS37-Q1
PRODUCTION DATA
The time delay (tCTR) can be programmed by connecting a capacitor between CTR1 pin and GND, CTR2 for channel 2. In this section CTRx represent either channel 1 or channel 2.
The relationship between external capacitor CCTRx_EXT (typ) and the time delay tCTRx (typ) is given by Equation 1.
RCTRx (typ) = is in kilo ohms (kOhms)
CCTRx_EXT (typ) = is given in microfarads (μF)
tCTRx (typ) = is the reset time delay (ms)
The reset delay varies according to three variables: the external capacitor (CCTRx_EXT), CTR pin internal resistance (RCTRx) 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:
The recommended maximum reset delay capacitor for the TPS37-Q1 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 to fully discharge during the duration of the voltage fault. To ensure the capacitor is fully discharged, the time period or duration of the voltage fault needs to be greater than 5% of the programmed reset time delay.