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AD736 RMS to DC converter

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Basically yes, within the specified accuracy limits.
 
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Thankyou,
We have three AD736 boards for measuring RMS current.
Today we found that all three of them have stopped working, after working for several months. They are giving nonsense outputs. We have a 10K resistor in series with the AC input (pin 2), and we find that our input AC signal is totally different at the pin side of this 10k resistor…and as you know, pin 2 is high Z, so there should be no difference in the signal either side of this 10k resistor.
Do you think it might be ESD?
We have been slack with use of wrist strap.
 

treez said:
Thankyou,
We have three AD736 boards for measuring RMS current.
Today we found that all three of them have stopped working, after working for several months. They are giving nonsense outputs. We have a 10K resistor in series with the AC input (pin 2), and we find that our input AC signal is totally different at the pin side of this 10k resistor…and as you know, pin 2 is high Z, so there should be no difference in the signal either side of this 10k resistor.
Do you think it might be ESD?
We have been slack with use of wrist strap.
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An overshooting ( any extreme case is possible such as inductive or capacitive overcharging on the network) on the AC voltage might be blown-up the IC.
 
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AC Input pin 2 should be high impedance 10^12 ohms, so if there is a drop across 10k input resistor, you have damaged the input op-amp. I suggest clamp diodes to protect pin 2. Like BAV99 to rails.
 
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Thanks, i must admit i am surprised the maximum RMS input is only 200mV for the AD736...Ooops, just read on, its 1Vrms for supplies above +/-5V
 
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Thanks, i must admit i am surprised the maximum RMS input is only 200mV for the AD736.
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Don't confuse maximum ratings and operation conditions. 200 mV is suggested rms level for low supply voltage, peak input voltage for +/- 15V supply that is converted into correct rms value is +/- 4V. Maximum rating is however +/- Vsupply.

I don't have AD736 at hand, but I guess that it has substrate diodes protecting Vin pin, the allowed maximum input current may be limited to a few mA however. Datasheet Fig. 25 is suggesting additional protection diodes and a series resistor.

I imagine that you can easily damage AD736 if you e.g. connect the output of a current transformer without protection and expose the circuit to inrush or short circuit current.
 

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