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# MAX6499 Overvoltage and Undervoltage Protection

2016-09-16 06:16
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TheMAX6499comprises undervoltage and overvoltage comparators for window detection. WHen the monitored voltage is within selected “window”, GATE is enhances and the n-channel MOSFET is on. GATE falls to OUTFB when the monitored voltage falls below the lower limit (V triplow) or exceeds the upper limit (Vtriphigh) of the window, turning off the MOSFET. The MAX6499 enabling the DC-DC converter when the monitored voltage is in the selected window is shown on the diagram below:

We can calculate the value of R1,R2,R3 as follows:

V triplow = (Vth-) )(Rtotal/(R2 R3))
V triphigh = (Vth ) (Rtotal/R3)
where Rtotal = R1 R2 R3

The values of R1, R2, and R3 can be found with this following steps:

Choose a value for RTOTAL, the sum of R1, R2, and R3. Because the MAX6499 has very high input impedance, RTOTAL can be up to 5MOhm.Calculate R3 based on RTOTAL and the desired upper trip point:R3 = (Vth x Rtotal)/VtriphighCalculate R2 based on RTOTAL, R3, and the desired lower trip point:R2 = [((Vth-) x Rtotal)/Vtriplow]-R3Calculate R1 based on RTOTAL, R2, and R3:R1 = RTOTAL – R2 – R3

Keep R3 <= 1kOhm? to improve ESD protection. The value of Vth- and Vth can be obtained from the datasheet. [Source: maxim-ic.com]