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

What maximum current is required on the AD7714 reference input (REF IN+)?  REF IN+ will be at 3.0V.  REF IN- will be at GND.  AVDD and DVDD will be at 3.4V.  I don't see this figure on the datasheet.

Ron

• 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.

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