About the solution EMC/EMI of AD421

Question

We are using to the AD421 parts on our industrial products and we are testing the EMC/EMI test for getting certification.

I'm trying to find the root cause about surge(IEC61000-4-5)/burst(IEC61000-4-4) for EMC because We are failing continue at surge/burst test item. (AD421 datasheet link: http://www.analog.com/media/en/technical-documentation/data-sheets/AD421.pdf)

We should solve the below Issue.

Status 1: The initial 4-20mA Output was 8mA. The AD421 have to output 8mA. But suddenly drop from 8mA to 4mA or increase from 8mA to12mA when testing Surge or burst. and output have recovered after about 1sec.

Status 2:This problem occurs too when the walkie-talkie operates on closely distance to AD421 .

Questions.

1. What condition occur this symptoms in AD421?
2. What is "POWER-ON RESET" in internal functional block diagram of AD421?

3. Could you give me the anything reference material of AD421 for the solving EMC/EMI?

Please help me about the way of solution for problem.

Answer 1

What condition occur this symptoms in AD421?

You are probably violating the absolute maximum ratings of the part, since you don't have a schematic, I'll take a guess as to what is going on: There is an overvoltage to the part, and you didn't protect the rails. Or there is an undervoltage for a short duration. Or the inputs go to an external device or antenna and you didn't put voltage limiting diodes to protect the inputs and outputs of the AD421

Drop a schematic in that answer and I'll update mine

What is "POWER-ON RESET" in internal functional block diagram of AD421?

From the datasheet:

"When REF OUT1 and REF OUT2 are used in application circuits, external 4.7uF capacitors are required on the reference pins to provide compensation and ensure stable operation of the references. These capacitors can be omitted if the internal refer- ences are not required. REF OUT2 is sensed internally, and if more than 0.5 mA is drawn externally from this reference, the chip goes into a power on reset state. In this state the sigma-delta DAC is disabled, the internal oscillator is stopped and the input data latch is cleared"

So you could be drawing more than 0.5mA from the Refout2 port. and that is shutting down the part. The first thing I would do is check your Vcc when preforming the surge test with an oscilloscope. I would also check your ground voltage vs an external ground.

Could you give me the anything reference material of AD421 for the solving EMC/EMI?

Yep, Its called Electromagnetic Compatibility Engineering