Digital Isolator for SPI Interface

Sharvy Mayan

Other Parts Discussed in Thread: ISO7341C, SN6501, ISO7841

Hi,

For our new project, we are planning to isolate the digital signal ( SPI Interface ) used in between a Micro controller & an ADC. Our isolation requirement is 1.5kV.

Supply voltage will be 3.3V or 5V.

Could you please suggest us the best Digital Isolator part number from TI, which is being used for the SPI Interface isolation.
Also please let me know, whether you have any Digital Isolator which isolates both data & power

Best Regards

Sharvy

over 9 years ago

0 Koteshwar Rao over 9 years ago

TI__Guru 55885 points

Hi Sharvy,

1. For an isolation voltage of 1.5kV you can use ISO7341C for isolating SPI Interface.
2. Currently we do not have a device that isolates both data & power. You can use SN6501 or SN6505 for isolating power.

Regards,
Koteshwar Rao

0 Sharvy Mayan over 9 years ago in reply to Koteshwar Rao

Intellectual 680 points

Hi,

Thanks for the feedback.

As you know that, for SPI 4 channels are there, 3 are Master outputs and one is input.

Suggest me the part number which support the above configuration, 3 Input & One output.
For SPI standard data rate / speed , the suggested part is good ISO7341C ?

Best Regards

Sharvy

0 Koteshwar Rao over 9 years ago in reply to Sharvy Mayan

TI__Guru 55885 points

Hi Sharvy,

Yes, ISO7341C has 3 inputs and one output and the device meets SPI standard datarates/speed. You can use this for SPI isolation.

Regards,
Koteshwar Rao

0 Sharvy Mayan over 9 years ago in reply to Koteshwar Rao

Intellectual 680 points

Hi,

Thank you very much.

Is there any specific requirement on the powers of VCC1 & VCC2 ( For ex- VCC1 should be greater than VCC2 or vice versa ) ?

Can I operate VCC1 with 3.3V and VCC2 with 5V?

Best Regards

Sharvy

0 Koteshwar Rao over 9 years ago in reply to Sharvy Mayan

TI__Guru 55885 points

Sharvy,

VCC1 & VCC2 can be anywhere between 3V & 5.5V independently. You can operate one of them at 3.3V and the other at 5V without any issues.
If you are looking for better propagation delays and other timing specs, you can also look at ISO7841 which is pin compatible with ISO7341C.

Regards,
Koteshwar Rao

0 Sharvy Mayan over 9 years ago in reply to Koteshwar Rao

Intellectual 680 points

Hi Koteshwar,

Thanks for the support

Best Regards
Sharvy

0 Sharvy Mayan over 9 years ago in reply to Sharvy Mayan

Intellectual 680 points

Hi,

I am re-opening this case again.
Our design is to use 8 individual Digital Isolator's ( ISO7341C ) for the Channel to channel isolation.
1. Do you have any idea about the SPI load driving capability?
2. What is the maximum loading to SPI line by the ISO7341C device?
3. Do I need any Fan out buffer to buffer the SPI channel from the MCU, since this single SPI Channel is branching to 8 ISOLATORS.
Best Regards
Sharvy

0 Koteshwar Rao over 9 years ago in reply to Sharvy Mayan

TI__Guru 55885 points

Hi Sharvy,

Please find below the answers for your questions.
1. SPI is based on bare digital lines and doesn't have any special electrical requirements hence Fan Out / Fan In of a device can be directly determined by the device IOH/IOL & IIH/IIL specs.
2. ISO7341C only requires a max/min IIH/IIL of +10µA/-10µA whereas the driving capability of ISO7341C is +4mA/-4mA (IOH/IOL).
3. Based on the IOH/IOL strength of MCU GPIOs, you can determine if a buffer is required.

Regards,
Koteshwar Rao

0 Sharvy Mayan over 9 years ago in reply to Koteshwar Rao

Intellectual 680 points

Dear Koteshwar,

Thanks for the feedback.

As per our MCU , the pin can source and sink up to +/-8mA.

Now I can figure out that, the MCU can directly feed the 8 Digital Isolators ISO7341C without any loading problem.

Best Regards

Sharvy

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Digital Isolator for SPI Interface