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Isolation with AD7401A in high noise environment

Question asked by JohnO on May 29, 2012
Latest reply on May 29, 2012 by AndyR

I'm considering use of a AD7401A for isolated DC link voltage measurement in a several hundred kW inverter.  Part specifications appear suitable, but the small signal range has me concerned, particularly considering the noisy environment it will operate in.  My preliminary plan is to implement a SINC3  filter in an FPGA with moderate bandwidth (10's of kHz), and use this signal for over-voltage protection.  Additional digital filtering, with a lower cutoff and notches at the switching frequency and harmonics would provide a signal for control use. The input signal will be derived from a high value divider, and produce a  source resistance of about 500 ohms unbalanced, or about 1k if I balance it.  I'll include a cap to put a pole just a little above the SINC3 cutoff.

 

1. Has this part been successfully used for this sort of application? 

2. Are there any special design considerations for use in a high noise environment.

3. With a 500 ohm source resistance, should the signal be buffered, or can the dynamic impedance be sufficiently compensated for using a minor gain correction factor?

4. Should I expect to get near datasheet performance, or is it likely that interference noise will dominate the measurement, even with the relatively low frequency filtering?

5. One physical implementation possibility puts this device on a gate driver board, which sits right on top of a high power IGBT.  I suppose this is where it would need to be located in a current sensing application, but I do have the option of getting it a few inches away from the switching nodes and high di/dt currents for some incremental cost increase.  How critical is this?

 

Thanks,

John

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