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A/D Reference Voltage Question

Discussion in 'Electronic Design' started by Thomas Roberts, Jul 15, 2003.

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  1. Typically, when dealing with common A/D converters (10 bit) can the AD
    Reference Voltage exceed the IC's supply voltage? Specifically, if the IC is
    powered via +5vdc, can the AD Ref Voltage be supplied with +24vdc as a basis
    for comparison?


    Respectfully,

    Thomas Roberts
     
  2. steve

    steve Guest

    I would suspect that driving the reference voltage above the positive is
    forbidden -- look for the absolute maximum input voltage levels called
    out on the device data sheet.

    There is likely to be ESD protection circuitry on the reference input
    pin that could become forward biased if you take the reference voltage
    above the positive rail (or below the negative rail).

    steve
     
  3. No. Usually Vdd + 0.3V to Vss - -0.3V (absolute max). It will probably
    work optimally with Vx < Vref <= Vdd, where Vx varies by chip design
    from perhaps 100mV (some delta-sigma converters and dual-slope
    converters) to about 2V, with a 5V Vdd.

    You can scale the 24V down to what you need with resistors and perhaps
    an op-amp.

    Best regards,
    Spehro Pefhany
     
  4. ddwyer

    ddwyer Guest

    No but you can get precision potential dividers from Vishay accurate to
    10ppm or so divide the reference voltage to = or below the IC supply
    voltage. Note that it is common to use a similar divider to reduce the
    max input voltage to be measured to = divided reference voltage.
    Normally 5V is the maximum supply for modern A/D converters.
     
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