Understanding IDAC ADS1248

Discussion in 'General Electronics Chat' started by aamirali, Dec 15, 2013.

  1. aamirali

    Thread Starter Member

    Feb 2, 2012
    415
    1
    I have some basic questions about IDAC:
    1. In data sheet of ADS1248, condition on using IDAC is (Vdd-0.7V) voltage compliance. I am using AVdd = 5V.
    What if I use 4K resistor & IDAC of 1.5mA. Theoretically it produces voltage of 6V. But it cannot happen.
    So what will happen actually in this case. Will it damage ADS1248.

    2. Suppose I use Avdd = 5V, res = 1333 ohm & IDAC = 1.5mA. Theoretically it will produce voltage of 2V across resistor. But since Avdd = 5V & Vres = 2V. So will rest of 3V come across internal transistor/mosfet across Vce/Vds. & dissipate power across it. Or Avdd is independent & voltage generated across resistor is independent. A internal diagram could make it easier, if available??
     
  2. antonv

    Member

    Nov 27, 2012
    149
    27
    Why do you need a resistor? Just feed the current to your RTD, thermistor or thermocouple.

    Why do you need to run at 1.5 mA? Use a smaller current if the voltage across the sensor will give you trouble.
     
  3. aamirali

    Thread Starter Member

    Feb 2, 2012
    415
    1
    I have successfully interfaced RTD. That is not the problem.

    I want to understand IDAC that's it.
     
  4. antonv

    Member

    Nov 27, 2012
    149
    27
    The IDAC is a constant current source so if your resistor is too large then the DAC will loose control of its output current: The output current will be equal to VDD-0.7/R. I don't believe it will damage the DAC.
     
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