AMC1200-Q1: Distorted output

Hello,

Thank you for your question. Without a schematic, it is hard to understand where this distortion comes from. Could you please include a schematic or detail what you are measuring so that we can better help? You could also try probing both output pins with respect to GND2.

There are references of what input vs output should look like for this device in the data sheet as well.

Best regards,

Eva

I enclose the schematic. For testing purposes, I scale down the utility grid voltage from 230 V to 30 V by transformers T1 and T2. Then, with voltage divider R1 and R2 I scale down the voltage to around 140 mV peak. R3, R4, C1 create filter to filter out (in future) inverter 40 kHz switching frequency. The AMC1200 is supplied from both side from independent channels of power supply (model: GPP-4323 Gw Instek). I measured the voltage I presented exactly on pins of the device. Red are for 1st photo, and green for 2nd photo. 

In the future there I will plan to transform the voltage to single-ended with offset of 1.65 V. 

Thank you for the answer. I connect two 10k resistors to VOUTP and VOUTN pins. I measure the voltage between resistors and I have still slightly distorted output.

when I measure it at the same pins but both with reference to GND and then subtract both values I receive:

 (light blue is subtraction)

What is interesting, when I connect eval board, the output is correct and there is nothing at the output of AMC1200.


My input are not tied to GND. I have only 10 pF caps between input pins and GND1. 

So I solder rest of the circuit (conversion to single-ended) and the output have the same shape:

The circuit looks as follows:

Okay, I grounded one of the input and it looks like it work! Thank you.

But still, you do not have your input grounded in the eval boards, and it works fine without grounding. DO you have any possible explanation?

One more thing, when I actually put it into the system and I measure output voltage of the inverter, after grounding inputs I have shift in common mode voltage, instead of 1V65, the whole waveform is above 1V65. 

When I measure exactly at the output pins of the AMC1200 the wave is already shifted.

Hi, offset that is visible on the oscilloscope is measured value. My question was why the waveform is lifted above 1.65 V like this:

Instead of be like this:

I want to 1.65 V be exactly the middle of the waveform.

Hello,
I have 1.65 V at pin 3 of OPA350. There is a voltage divider with two 10 kOhm.

Hi, the output before the resistors is already shifted a bit:

I measure the resistance and even replace just in case the resistors. Everything is correct. Before applying the voltage, the voltage is equal to 1.65 V, as it should be, the wave is shifted only after applying the voltage.

Hi, I verify and pin 3 and 6 have correct 1.65 V. I removed C8, but it does not help. Anyway, I am waiting now for new design of the board with already grounded input, not by jumper cable as I am doing it right now. I will come back to this issue in the middle of December. Thank you for helping so far.