ISO1644: SPI Interface

Bryan McLaughlin

Part Number: ISO1644
Other Parts Discussed in Thread: ISO7741,

Do you have any advice or information about using the ISO164x in a 4 wire SPI application? I'm interested in it primarily for I2C but would love to have the option to use it for SPI as well.

Any issues with the following mapping for 4 wire SPI?

SCL = MCLK

SDA = MOSI

GPIO.A = /CS

GPIO.B = Not used

GPIO.C = MISO

over 1 year ago

+1 Andrew J over 1 year ago

TI__Mastermind 29415 points

Hello Brian,

The following mapping would work, however, please note that SCL and SDA are open-collector outputs will need a pull-up resistor in the SPI application. Typically, ISO7741 is our normal recommended part for 4-wire SPI applications.

Best,
Andrew

0 Bryan McLaughlin over 1 year ago in reply to Andrew J

Expert 1110 points

Thanks Andrew. We might need to configure between being an I2C or SPI bus dynamically, so this is very cool that the ISO164x can basically do either.

+1 Andrew J over 1 year ago in reply to Bryan McLaughlin

TI__Mastermind 29415 points

Hello Bryan,

Glad to hear that you are interested, a colleague pointed out that we have product overview for this application: Isolating I2C Plus SPI Signals.

We would recommend not using SDA and SCL for MCLK or MOSI since open-collector outputs with external pull-up resistors are very slow. You can use SDA and SCL as /CS since the chip-select signal is a slower data signal.

ISO1644 supports 3-wire SPI but if you can use SDA or SCL for /CS, then 4-wire SPI support is possible.

I hope this helps.

Best,
Andrew

0 Bryan McLaughlin over 1 year ago in reply to Andrew J

Expert 1110 points

That's a great idea since /CS is slower. It would be great to have more no-lead package parts available for functional isolation <50V for breaking GND loops on sensor applications like this.

Isolation

Isolation forum

ISO1644: SPI Interface