# Understanding IDAC ADS1248

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

1. ### aamirali Thread Starter Member

Feb 2, 2012
415
2
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
2
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.