Galvanic isolation for ADC front end circuit

Chitharanjan M1

Other Parts Discussed in Thread: ADC34J44, ISO7741, AMC3306M25

Hi,

We have a new requirement on ADC with the below specification, and we have chosen "ADC34J44"(JESD204B interface) part which is suitable for out requirement . The concern is ADC input should be galvanically isolated and can you please suggest the front end circuit or differential amplifier which is suitable for ADC34J44 analog input?

Channel -4nos

Sample rate - 125Msps

Analog Input -4-20mA( galvanic isolated)

Regards,

Chitharanjan M

7 months ago

0 Andrew Jackiw 7 months ago

TI__Genius 13505 points

Hello Chitharanjan,

Thank you for reaching out.

To isolate an ADC there are a few options. To isolate the digital signals, you can use a digital isolator like ISO7741. Alternately, I believe ISOM8110 would be able to support isolation of a single 4-20mA signal.

The other option would be to use an Isolated ADC. Which sounds like it may be a better option for you application.

Let me know if you have further questions.

Best,
Andrew

0 Chitharanjan M1 7 months ago in reply to Andrew Jackiw

Intellectual 360 points

HI Andrew,

I have got one isolated ADC AMC3306 part which is having integrated galvanic isolation in it.

Can you please confirm, is this support 4-20mA analog current input?

Regards,

Chitharanjan M

0 Andrew Jackiw 7 months ago in reply to Chitharanjan M1

TI__Genius 13505 points

Hello Chitharanjan,

Let me notify the isolated ADC product line for more information.

Best,
Andrew

0 Chitharanjan M1 7 months ago in reply to Andrew Jackiw

Intellectual 360 points

Sure, Also can you share me the reference design of AMC3306 where it is interfaced to 3 and 4 wire transmitter.

Regards,

Chitharanjan M

0 Chitharanjan M1 7 months ago in reply to Chitharanjan M1

Intellectual 360 points

Chitharanjan M1 said:
I have got one isolated ADC AMC3306 part which is having integrated galvanic isolation in it.

Can you please confirm, is this support 4-20mA analog current input?

Hi Andrew,

Can you please confirm on this?

Regards,

Chitharanjan M

0 Alexander Smith 7 months ago in reply to Chitharanjan M1

TI__Mastermind 47625 points

Hi Chitharanjan M,

AMC3306 is an isolated modulator that operates with up to a 20MHz clock. This device would not be suitable for a signal chain that requires 125Msps.

As Andrew said, isolating the digital signals will be necessary with the ADC on the high side.

0 Chitharanjan M1 7 months ago in reply to Alexander Smith

Intellectual 360 points

Thanks Alexander, Is TI have any ADC and DAC IC which meets below requirement if so please suggest the part

ADC -

4-20mA current Input with Maximum Sampling rate (>25MSPS)

12 or 16Bit

DAC-

4-20mA current Output with Maximum Sampling rate (>25MSPS)

12 or 16Bit

Regards,

Chitharanjan M

0 Chitharanjan M1 7 months ago in reply to Chitharanjan M1

Intellectual 360 points

Chitharanjan M1 said:
I have got one isolated ADC AMC3306 part which is having integrated galvanic isolation in it.

Can you please confirm, is this support 4-20mA analog current input?

Hi Alexander,

Can you please confirm on this?

Regards,

Chitharanjan M

0 Alexander Smith 7 months ago in reply to Chitharanjan M1

TI__Mastermind 47625 points

Hi Chitharanjan M,

Yes - this part is capable of measuring the voltage formed by the 4-20mA current flowing through a sensing resistor.

However, like I said in my previous post, it cannot meet the >25MSPS requirement.

Please see our high speed ADC product selection table here for assistance with selecting a high speed ADC: https://www.ti.com/data-converters/adc-circuit/high-speed/products.html

0 Chitharanjan M1 7 months ago in reply to Alexander Smith

Intellectual 360 points

Thanks Alexander Smith,

Alexander Smith said:
Yes - this part is capable of measuring the voltage formed by the 4-20mA current flowing through a sensing resistor.

Do you have a any reference design where AMC3306 has been used to measure 4-20mA current. If so please share the same.

Also please confirm on, Is the AMC3306 support 21MSPS? because I have not seen this number in the datasheet which is mentioned 78kSPS.

Regards,

Chitharanjan M

0 Alexander Smith 7 months ago in reply to Chitharanjan M1

TI__Mastermind 47625 points

Chitharanjan M,

The AMC3306 cannot support 21MSPS.

0 Chitharanjan M1 7 months ago in reply to Alexander Smith

Intellectual 360 points

Hi Alexander Smith,

What is the sample rate it can support?

Regards,

Chitharanjan M

0 Alexander Smith 7 months ago in reply to Chitharanjan M1

TI__Mastermind 47625 points

It will depend on the sigma delta filter settings. Please read this application note for additional information: https://www.ti.com/lit/wp/sbaa359a/sbaa359a.pdf?ts=1695734251576

0 Chitharanjan M1 6 months ago in reply to Alexander Smith

Intellectual 360 points

HI Alexander,

Can you please let me know whether AMC3306 ADC I can use it for 3 wire and 4 wire application?

If so what is the front end circuit to be used ? can you please share us the reference design where AMC3306 is used in 3 and 4 wire application?

Regards,

Chitharanjan M

0 Andrew Jackiw 6 months ago in reply to Chitharanjan M1

TI__Genius 13505 points

Hello Chitharanjan,

AMC3306M25 takes a differential analog input. Depending on how you condition the signal, AMC3306 should be able to be used in a 3 wire or 4 wire application depending on your support circuitry.

Please note that if you choose to use a non-isolated ADC and then isolate the digital signal using a digital isolator (for example isolated SPI) please use ISO7741.

Best,
Andrew

0 Chitharanjan M1 6 months ago in reply to Andrew Jackiw

Intellectual 360 points

HI Andrew,

Thanks for the detail....

Andrew Jackiw said:
AMC3306M25 takes a differential analog input. Depending on how you condition the signal, AMC3306 should be able to be used in a 3 wire or 4 wire application depending on your support circuitry.

Can you please let me know what type of front end circuit to be used for AMC3306M25? Is there any recommended filter circuit or directly I can connect the input from shunt resistor to AMC3306M25 input? and What is the recommended support circuitry for 3 or 4 wire configuration?

0 Andrew Jackiw 6 months ago in reply to Chitharanjan M1

TI__Genius 13505 points

Hello Chitharanjan,

This product is supported by Alex Smith. He should be able to assist your questions.

Best,
Andrew

0 Chitharanjan M1 6 months ago in reply to Andrew Jackiw

Intellectual 360 points

HI Alex Smith,

Regards,

Chitharanjan M

0 Alexander Smith 6 months ago in reply to Chitharanjan M1

TI__Mastermind 47625 points

Hi Chitharanjan M,

Please see the link below to reference collateral for our isolated data converters. The device datasheet is also a helpful resource.

Yes, you can connect a shunt resistor to the input of the AMC3306M25. There is no recommended circuit for a 3 or 4 wire configuration.

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1164993/faq-isolated-data-converter-collateral-overview

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Galvanic isolation for ADC front end circuit