AMC1200: AMC1200 wrong operation

the circuit is as below....

Hi pil joo huh,

Your diagram still did not come through.  Can you try to re-post it again?

Hi PJ,

click the "Insert File" button (paper clip) in the header of input box.

Kai

AMC1200_CIRCUIT_20200608.pdf

Hi PJ,

Thanks!  It came over that time!  You are violating the common mode input to the AMC1200.  As noted in the datasheet, normally the IN(-) node is referred to GND1 (5G1 in your schematic). Is the input actually an AC signal or is it really DC?  I ask because your outputs appear to be AC coupled.  What sort of application is this?

Dear TOM

First  Input Voltage is two Case

The one is DC mode(-50V ~ 50V) and the other is AC mode(0~300V).

We apply to Voltage monitor system.

In DC mode, it works normally by itself, but if  +50V and -50V are input  two amc1200 parts simultaneously, it occur problem.

If we want to negative voltage monitoring system,

do you recommend how to design method ?

refer to attached fileAMC1200_BLOCK_DIAGRAM.pptx

Thanks and BR

PJ

Dear TOM

Thanks for your cooperation.

I will test that your advise.

After testing, I will inform to you.

Thanks and BR

PJ

Dear Tom

we have tested that split resistor(7.5K and 7.5K), the result is bad(still amc 1200 is damaged(amc1200 is abnorma operation)

So, we are trying to input the amc1200 by changing the input voltage from negative to positive by adding a differential op amp to the front of the amc1200 input.

Is this circuit is normal operation?
If possible, could you recommend differential op-amp.

Thanks and BR

PJ

negative_dc_mode_improve.pptx

Dear TOM

What are your think about applying INA828 as a differential amplifier?

Thanks and BR

PJ

Hi PJ,

You can't tie the input of the AMC1200 to 5V like that, this might be the reason why the output is always saturated.  If you have two AMC1200 devices in circuit and they are both tied to two input sources, they will both see +/-50V, so perhaps I don't understand what it is that you are trying to accomplish.  Can you perhaps describe the intended application?

OK, so the circuit I originally suggested would work I believe.  If you only need to verify polarity swap, you could do this with one isolation amplifier and and follow that with a comparator circuit.

Hi Pil Joo Huh,

do you actually need to measure the 24V / -24V or do you only need to detect the presence of one of these voltages? In the latter case you could use simple optocouplers.

Kai

Dear TOM

Thanks for your cooperation.

I have two question

1. According to your suggested circuit, Should I use two AMC1200 parts?
  We need to measure from positive 24V to negative24V power with only one AMC1200 part. Is it possible?
  In other words, VM1 and VM2 output is same graph (positive linear).

2. According to your output graph, VM2 output is from -950mV(in -24V) to 950mV(in +24V).
  But we want to output that 0mV(in -24V) to 950mV(in +24V), Is it possible?

Hi PJ,

Yes, you could use just one AMC1200 for this.  Just remove either device in the schematic above and then apply VINp to the R1/R2 node and VINn to the R3/R4 node.  Change the resistor values as needed to get FS+ and FS- voltage from the output.

Dear TOM

I have tested your recommended circuit.
(refer to attached file)
However, the test results were bad.
First, the AMC1200 positive input voltage (Vi +) is very high.
Vi + = 149mV (input = 24V) according to the partial pressure calculation.,
However, the actual measured values ​​are
 Source voltage = 0.5V, Vi + = 177mV
 Source voltage = -0.5V, Vi + = -177mV
I don't know the cause of this problem.
In my opinion, 24V_GND is not connected (so it looks like 24V_GND is floating).
Can you check this and advise to me?

Thanks and BR

PJAMC1200_CIRCUIT_20200707.pdf

Hi PJ,

If its OK with you, I'll send you a note to your e2e registered e-mail account and we can take this off line until I get a better idea of exactly what your setup looks like. 

Dear TOM

it is ok. I hope that it is solved ASAP.

Thanks and BR

PJ

AMC1200_CIRCUIT_20200709(AC MODE).pdfDear TOM