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AMC1200-Q1: Input side DC power supply grounding

danienpark
Prodigy 85 points
Part Number: AMC1200-Q1
Other Parts Discussed in Thread: AMC1200

Hi Support team,

I connected LEM LV25P voltage sensor and AMC1200Q1 for voltage measurement. 

I have two power supplies each has 4 channels, one DC power supply is for LV25P (VCC1, VCC2, GND1), and the input side of AMC1200 (VDD2, GND2, the other one is for the output side of AMC1200 (VDD3, GND3).

I obtained +15, -15 and GND1 using two channels of the power supply as in the figure. The input of LV25P is 100V AC sine and there is a measurement resistor in the output (R1 22). As I know that the input of AMC1200 is differential and so I measure differential voltage using AMC1200. One of R1 pin is connected to GND1 and VINN pin of AMC1200, the other pin of R1 is connected to the output of LV25P and VINP pin of AMC1200 as in the attached figure. I set up the experimental model of the circuit.

GND1 and GND2 come from the same DC Power supply,

First, I connected to these common pins as in the picture. I measure the differential rms voltage of the output (VOUTP-VOUTN) using a multimeter, and also I used math function of the oscilloscope to get the differential voltage (CHN1-CHN2). The results are the same, there is no problem. 

Second, I connected to GND1 and GND2. The results are the same as in the first scenario. 

My question is, should I connect GND1 and GND2 to each other or they should be separate. Because ı will make PCB circuit, before it, I want to be sure about these connections. 

Looking forward to your help folks, 

Best regards, 

danien.

  • 0
    Guru 140200 points

    Hi Danien,

    I would connect GND1 and GND2 on the board as shown in the second figure. I would use a local ground plane for these connections.

    But may I ask why you need double galvanic isolation? Doesn't already provide the LV25P galvanic isolation?

    Kai

  • 0 in reply to kai klaas69
    Prodigy 85 points

    Hi Kai,

    Thank you for your response.

    So it will not be a problem right, such as common-mode voltage etc.. ?

    I measure 175V p-p RMS AC sign using LV25 voltage measurement circuit. The output of this circuit is proper for AMC. So I just used AMC1200 with LV25P with this circuit. There is no specific reason. Actually, only AMC1200Q1 can be used for voltage measurement, I do not need extra voltage sensor. 

    I thought that two galvanic isolation will not be a problem in the DSP side ( low side of AMC1200), I hope it is right thought?

    danien

  • 0 in reply to danienpark
    TI__Guru 50151 points

    Hi Danien,

    To ensure that the common-mode voltage is valid for the AMC1200, we want VINN to be connected to the high side GND, GND2 in your schematic. Since the output voltage of the LEM is ultimately with respect to GND1, we want GND2 to equal GND1 as well. 

    Isolation barriers are not free, if you do not need double isolation (galvanic) then I would not recommend a galvanically isolated design for cost reasons. There is no issue for the DSP in this configuration though. 

    Thanks Kai! 

  • 0 in reply to Alexander Smith
    Prodigy 85 points

    Hi Alexander, 

    Many thanks for your and Kai's valuable informations.

    Best regards,

    Danien.