• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 46 subscribers
  • Views 700 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Understanding IDAC ADS1248

Aamir Ali
Expert 2525 points

Other Parts Discussed in Thread: ADS1248

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?? 

  • 0
    TI__Guru** 113765 points

    Hi Aamir,

    You cannot exceed the compliace voltage with the IDACs, so the current source will not longer be able to maintain constant current which the compliance voltage is reached.  You will not get the expected output once you reach the compliance voltage , but you will not damage the ADS1248.

    The IDAC is a current source that is generated from the AVDD supply.  This is why there is a compliance voltage restriction as there needs to be a source (AVDD), and a mechanism to keep the current constant.  As there is some overhead to create the current source, you cannot create a voltage with the IDACs all the way to the supply.  The outcome is simply Ohm's Law V=I*R up to the compliance voltage, which also can be described as I*R<= Compliance Voltage.

    So V=I*R and V must be <= Compliance Voltage.

    Best regards,

    Bob B