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Discussion in 'Electronic Design' started by john, Aug 25, 2005.

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  1. john

    john Guest

    Hello,

    Has anybody worked with the analog Digital to analog converter
    AD5532HS? If yes please let me know. I am having some problems with its
    offset_in and Ref_in pins.

    Thanks
    Regards
    John
     
  2. PeteS

    PeteS Guest

    Exactly what problems are you having? I've used one of the same family,
    and although I had no real problems, you have to be a little careful
    about source impedance on those pins.

    Cheers

    PeteS
     
  3. john

    john Guest

    Hello,

    The ouput of the DAC is going to the non- inverting input of an op amp.
    Now, when I apply 2.5 volts to the " Ref_in" and " "Offset" pins of the
    DAC, the DAC outputs -2.4 volts , and in return my opamp outputs the
    -15 volts. Opamp has dual power supply of + - 15volts. The inverting
    input of the opamp is grounded.
    I need to output zero from this DAC at the power up when its not
    getting any digital data. Please advice
    thanks
    Regards
    John
     
  4. PeteS

    PeteS Guest

    I am not sure you understand the functioning of the DAC. Vref in
    requires a stable 2.5V reference. Whether you want to apply that to the
    Offset in pin is another matter.

    The DAC outputs a nominal 5V span, and applying 2.5V to the Offset in
    pin sets the output range at -2.5 to +2.5. Note that if you are only
    going to -2.4V, your supplies to the DAC may be a little low (it can
    only get within 2V of the power supply rails)

    The output is -2.5V for a code of 0 and +2.5 for a code of 0x3FFF (14
    bit device) with Voffset = 2.5V. It would be 0V for a code of 0 with
    Voffset(in) = Ground, and 5V (assuming your power supply is >7V for the
    analogue section) for a code 0f 0x3FFF. If you just turn the device on,
    I would expect it to have 0 in the DAC register, so you could expect
    the output to be at the negative maximum.

    The output voltage of the device is given by:

    Vo = 2 x V(DAC) - V(offset_in)
    Where V(DAC) = [Vref(in) x Code] / 2^14

    If you want to output zero from the device at power up, then tie
    Voffset(in) to ground.

    Cheers

    PeteS
     
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