AMC1351: Isolated Analog Input

NANDHA KUMAR

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

over 1 year ago

0 kai klaas69 over 1 year ago

Guru 140200 points

Hi Nadha,

your schematic doesn't show the AMC1351.

Kai

0 NANDHA KUMAR over 1 year ago 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 Tom Hendrick over 1 year ago in reply to NANDHA KUMAR

TI__Guru**** 171966 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 NANDHA KUMAR over 1 year ago 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 Alexander Smith over 1 year ago in reply to NANDHA KUMAR

TI__Mastermind 49071 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 NANDHA KUMAR over 1 year ago 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 Alexander Smith over 1 year ago in reply to NANDHA KUMAR

TI__Mastermind 49071 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 NANDHA KUMAR over 1 year ago 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 Alexander Smith over 1 year ago in reply to NANDHA KUMAR

TI__Mastermind 49071 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.

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AMC1351: Isolated Analog Input