max current is required on the AD7714 reference input (REF IN+)?

Hi, Ron.

For AVDD = +3 to +3.6, VREF should be +1.25 V. Therefore, if REFIN(-) is at GND then REFIN(+) should be +1.25 V since VREF = REF(+) - REF(-). But you stated REFIN(+)=3 V, can you check this?

We'll get back to you about the maximum current on the REFIN inputs.

Regards,

Johnny

We are using one of the Y parts, so it looks like the maximum VREF is 1.75V.  Is that how you see it?  We were planning to use a 3V reference, so looks like this is not going to work.  I'm glad I asked the question.  Had not noticed this before.

Ron

One of my colleagues says that he consulted with Analog Devices and they said that it was ok to use a 3V reference with a supply voltage of 3.4V.  Does that sound possible?

Ron

Hi, Ron.

If you're looking to its absolute maximum ratings, yes, you can use 3 V for REFIN with a supply voltage of 3.4 V. My concern here is the accuracy of your system since VREF goes higher than what is the normal value. I have tried the Temperature Demo of AD7714 Eval Board and it reads more than 80 deg Celsius using REFIN+ = 3 V with an AVDD = 3.3 V. The normal temperature reading should be 21 deg Celsius with REFIN+ = 1.25 V for our setup in this case.

By the way, REFIN inputs have passed +/-100 mA current stress test which means that the device can still work properly with this amount of source/sink current. But at 260 mA, the device may behave strangely as it has reached its limit.

Please don't hesitate to ask if you require anything else.

Regards,

Johnny

Thanks for the info on the reference.  We are designing a power supply for the 3V reference, which will supply several ICs, and need to know the current that can typically be expected into REFIN+.  It's not going to be 100 or 260 mA is it?

Thanks

Ron

Hi, Ron.

I have checked the AD7714 evaluation board. Voltage is applied on the REFIN+ pin and current is measured. Typical current is 0.36 uA to 1 uA for REFIN+ voltage of 1.23 V to 3.3 V with roughly 0.03 uA increase for every 0.1 voltage step. The values were consistent for the 2 devices tested.

Regards,

Johnny

Thank you ferdi.  That's not much.

Ron