I have a simple comparator circuit I was planning to use for a 2-cell Li battery. I'd like to cut the voltage off at around 2·2.8 V = 5.6 V.
To accomplish this I have the circuit below, but just a little bit of noise in the battery voltage and it will cause my comparator (which drives a P-MOSFET) to oscillate between high and low output.
So I'd like to add some hysteresis. I found a good article about this. During good battery voltages I want the output of the comparator to be GND. I believe I have the correct configuration for this.
I would like to add approximately 0.5 V of hysteresis such that once I transition into bad battery voltage at 5.6 V I need to make it to 6.1 V again before I can close the load circuit again.
For hysteresis calculations I will assume the Voh (output high) is 7.4 V and Vol is 0 V. But I need to select a value for either R1 to solve for R2 or vice versa. How can I go about selecting a resistor value?
Datasheets:
TLV3401IDR
MAX6043BAUT25+T
Best Answer
1º point: Looking at the Analog Devices post I think that the circuit that works for you is not the one in figure 3 but the one in figure 5 the single supply inverting hysteresis understanding that you want to power the comparator only with the battery.
2º point: I find the math functions of the AD post complicated, but in this Texas Instrument file they present the functions in a simpler way for that circuit in section 2.1 (page 7) and I ended up with this circuit, the only thing I change is the reference voltage from 2.5 to 3.3V and the circuit use E12 standard resistors values.
Vl = 5.6V / 2 = 2,8V ||| Vh = 6.1V / 2 = 3.05 ||| Vref = 3.3V
*The resistor values of 1.12M are not stadard, I take 1,2M from E12 standard series values.
simulate this circuit – Schematic created using CircuitLab
The behavior of the circuit should be similar to this: