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Voltage monitor MAX6457 problem

Discussion in 'Electronic Design' started by [email protected], Aug 15, 2007.

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  1. Guest

    Dear group:

    I am using the Li-Ion battery (7.4V nominal) to power my circuit. I
    need to monitor the battery volgate and shut down the whole thing when
    it drops below 6V.

    I am using MAX6457 to monitor the voltage. The datasheet is here:

    I have trouble selecting values for the resistors R1 and R2. According
    to the equation on
    page 8, you should fix R2 and than set R1 = R2 (Vtrip / Vth - 1). I am
    really confused, what are the values of Vtrip and Vth in my
    case... not very clear from the datasheet. I know I can select these
    resistors by trial and error but I have to demostrate devising the
    correct values according to the datasheet. Thanks in advance.
  2. Fred Bloggs

    Fred Bloggs Guest

    Vtrip=6V (low Vbatt level) and Vth=Vth(-), the monitor will pull open
    drain OUT low when Vbatt *falls* below 6V. Depending upon the grade of
    6457 as designated in the suffix as A, B, or C, the Vth(-) will be 0.5,
    5, or 8.3 % respectively below Vth nominal of 1.228V. This means you use
    Vth=0.995x1.228, 0.95x1.228, or 0.917x1.228 for Vth in the equation. The
    nominal Vth reference varies +/-2% over parts and temperature.
  3. Guest

    Thanks a lot! If it works, you saved my day :)
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