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AMC1351: Isolated Analog Input

NANDHA KUMAR
Prodigy 90 points
Part Number: AMC1351
Other Parts Discussed in Thread: ISO1410, , AMC3330

Dear Team,

We need Isolated analog input for our application. Already we have a Power & Signal isolated RS485 section on our Design. please refer below Schematic 

Here MCU is there in the input side of ISO1410 which is the system GND of PCB ( C_GND ). Here we want to introduce single output analog voltage sensing circuit to measure analog voltage in the range of 0 to 5v. 

On AMC1351 can we connect GND1 & GN2 to each other? because the isolated output ( From AMC1351 ) needs to be measured by MCU on the system GND. Will this isolator work for this application?

If not, kindly suggest an approach/part have isolated analog input without 2 different GND requirements  ( like Optocoupler for digital signals ).  

Also, we have 2 analog inputs in our application. so if there is any 2-channel IC that will be more helpful. 

Awaiting your response. Thanks

  • 0
    Guru 140200 points

    Hi Nadha,

    your schematic doesn't show the AMC1351.

    Kai

  • 0 in reply to kai klaas69
    Prodigy 90 points

    Hello Kai

    The attached schematic is our existing RS485 isolated section & MCU only for your reference. 

    My query is, Can we short GND1 & GND2 of AMC1351 to achieve our isolated analog input application? 

    We need a solution to sense Analog voltage 0 to 5v by MCU which is there in the above circuit ( System GND ). 

  • 0 in reply to NANDHA KUMAR
    TI__Guru**** 176541 points

    Hi Nandha,

    You could short GND1 and GND2 together, but then you would loose the isolation capabilities of the AMC1351.  Can you pencil in the AMC1351 to your drawing so that we have a better idea what it is that you are trying to do?

  • 0 in reply to Tom Hendrick
    Prodigy 90 points

    Hi Tom,

    Please refer to the schematic reference which you asked 

    Here since our MCU is there at system ground we are in a situation to give isolated analog input to the same MCU on system ground. Due to that, we can't maintain 2 different GND planes for this. So if there is an Analog optocoupler then that will be very helpful for our application. 

  • 0 in reply to NANDHA KUMAR
    TI__Guru 52722 points

    Hi Nandha,

    You need a separate high side ground in order to have an isolated measurement. As you've drawn with both device grounds connected to the same plane, the isolation barrier that the device provides is bypassed. 

    I recommend looking at the AMC3330, as it is capable of voltage measurements and provides it's own isolated DC/DC converter which simplifies the design. It will need it's own localized ground connection. 

  • 0 in reply to Alexander Smith
    Prodigy 90 points

    Dear Alex,

    Noted with thanks, We will explore the same ( AMC3330 ). 

    Meantime do we have any Analog optocoupler parts in our gallery?  

  • 0 in reply to NANDHA KUMAR
    TI__Guru 52722 points

    Hi Nandha,

    We mainly produce capacitive and hall based isolators - but we have recently released an "Opto-emulator": https://www.ti.com/product/ISOM8710

    I am not familiar with this device. 

  • 0 in reply to Alexander Smith
    Prodigy 90 points

    Hi Alex,

    We introduced different Gnd planes on the design now. Please review the below schematic and share your comment,

    AMC1351

    ISO_GND = Isolated ground plane

    Sys_Gnd = System Gnd for all other peripherals. 

  • 0 in reply to NANDHA KUMAR
    TI__Guru 52722 points

    Hi Nandha,

    In general it looks OK with the exception of the AMC1351 negative output being tied directly to ground, this pin is driven and direct connection to ground can damage the device. At least, I recommend termination to ground through a 10k resistor to limit the output current. Performing a differential to single-ended conversion close to the MCU ADC is preferred. You can see an example of such a conversion here: https://www.ti.com/lit/an/sbaa347/sbaa347.pdf

    Please post again once the schematic is finalized and I'll take a closer look.