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THS4521: When collecting the waveform of IEC61000-4-18 damped oscillatory , it was found that the power supply of THS4521 was disturbed.

user4973896
Expert 1555 points
Part Number: THS4521
Other Parts Discussed in Thread: THS4551

When applying the common mode (L to PE or N to PE) 2500V 100KHz damped oscillation wave interference to the input power supply AC220V of the tested board, use the above circuit to collect the 5V power output on the tested board which is generated by the ac220v through the isolated power module. The power supply of the THS4521  was also disturbed. This prevents the waveform from being acquired.

The signal connection method is: connect the 5V+ of the tested board to the 5V network of the test board； and directly short the negative of 5V of the tested board (that is, the GND of the tested board) and the gnd of the test board.

Someone told the circuit where there is a problem, how to modify it？

  • 0
    Guru 48395 points

    Lots of little things here - 

    1. Your Vref_buf appears to go to the FDA Vocm control, but then the same line is connect to ground just below there. 

    2. you need to match the impedances better on the two sides - your big attenuator shows 1.05k looking back from inverting node, set lower Rg to 1.05k also

    3. You should use the much improved drop in upgrade to the THS4521 - the THS4551

    4. You may need to attenuate more - if you power input is really 2500V, that is about 6.23V out of the attenuator. At gain of single to diff (assuming Vref-Buf is 1.65V) will be +/- 1.55V around that Vocm - that is barely in range for output swing.