TPS37 datasheet(28/48 Pages) TI

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to operating frequency. Input to SENSE2 of TPS37A will monitor the AC source by using a "resistive-drop"

supply topology circuit. The unique circuit resistively divides the AC voltage signal and provides only the positive

half wave Figure 10-5 into SENSE2 input. The half wave signal does not go through any output filter and hence

any change to the AC voltage or operating frequency can be rapidly detected. Knowing the operating frequency

of the AC source and converting to the time domain, the TPS37A SENSE2 delay can be programmed, by the

capacitor on CTS2 pin, to equal or be greater than one-half of the operating period (the frequency of the half

wave rectification signal) or the half cycle shown in Figure 10-5. When the half wave voltage amplitude falls

below the SENSE2 threshold voltage, the SENSE2 time delay counter begins to increment. If the next half wave

voltage amplitude exceeds the SENSE2 threshold voltage, the SENSE2 time delay counter will reset and the

TPS37A RESET2 pin will indicate no fault was detected. Conversely, if the voltage amplitude of the half wave

does not reach the SENSE2 threshold voltage within the programmed time delay of tCTS, a fault will occur.

Also, a fault can occur if the operating frequency from the AC source decreases, resulting in lower AC voltage

amplitude at the programmed time delay tCTS.

AC Early Fault Flag (RESET2)

FC = 1.25 ms

Half Cycle

CTS

Half Wave (SENSE2)

Full Cycle

HC = 0.625 ms

CTS

≤ tHC

Figure 10-5. Design 2 Timing Diagram

The TPS37A, with its ability of having a wide VDD range from 2.7 V to 65 V and under and overvoltage

detection, offers a unique “window operating” AC power rail monitoring solution. Combining SENSE delay

feature with the "resistive-drop" supply circuitry, detecting an undervoltage event on the half cycle of the AC

power rail provides a fast power fault response. Likewise, the TPS37A provides an overvoltage monitoring and

SENSE delay fault detection for the same AC power rail. With under and overvoltage supervision of the AC

power rail, applications needing a specific operating DC range to protect its subsystems is achieve through

TPS37A. Good design practice recommends using a 0.1-µF capacitor on the VDD pin and this capacitance may

need to increase if using an adjustable version with a resistor divider.

Note that this design solution is not isolated and one must take into account when planning to use in high power

systems.

TPS37

SNVSBJ1D – OCTOBER 2020 – REVISED DECEMBER 2021

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TPS37 Datasheet(PDF) 28 Page - Texas Instruments