Undervoltage Lockout TLV7031

Question

I try to implement an undervoltage lockout trigger, when the supply voltage falls below a threshold voltage. The trigger itself should activate a gate driver, when there is enough voltage and below the threshold, it should be deactivated. A hysteresis is really important to prevent switching the power on and off to the gate driver, which can lead to destruction.

A comparator is the solution for this and I decided to take a TLV7031(Here). I have a power supply of 48VDC and want to trigger the undervoltage lockout at around 31VDC with at least 4VDC hysteresis. My solution looks like this, but I am unsure, if this will work, since I don't use comparators a lot:

R35 can be ignored, this is only to permanently activate the comparator output. The trigger voltage is 1.65VDC, which is (180kOhm + 10kOhm) / 10kOhm times the voltage for the power supply, that means 31.35VDC. The hysteresis is 3.3VDC * Rb/Ra = 0.2245, which is on the power supply side an equivalent voltage of 4.26VDC.

Are my calculations correct?

Edit: I did a simulation with a different comparator (LT1716) and it seems to work. Is this a standard non-inverting Schmitt Trigger circuit for any comparator?

Answer 1

I'm not sure if the default LTspice package comes with any TLV parts, but mine has a TLV3491. Here is what that does in this circuit:

With input voltage modeled as a triangle (green), it allows the FET gate (red) to go high at about 35.3V, and keeps it high until about 27.2V. Of course this could be different with your different comparator.

Answer 2

whether the one you have used is an open collector type TLV7031 comparator, then you will need some pull up resistor to 3.3V rail too for the bias!