TWIM not achieving 400 kbps

RE: TWIM not achieving 400 kbps

adamsperry — Mon, 14 Jun 2021 19:20:00 GMT

Thanks, this is great info.

RE: TWIM not achieving 400 kbps

Håkon Alseth — Mon, 14 Jun 2021 06:19:54 GMT

There was a article on this subject of varying i2c resistors, but it has apparently gone down.

I found a pdf'ed version of it here: https://www.thebackshed.com/forum/uploads/BobD/2013-01-26_175209_I2C_-_Effects_of_Varying_Pullup_Resistors.pdf

4.7k is generally a ok value for 400 kHz, you can usually go higher (5.6k) and lower (3.3k) without issues wrt. the wanted frequency.

Kind regards,

Håkon

RE: TWIM not achieving 400 kbps

adamsperry — Fri, 11 Jun 2021 17:26:13 GMT

That did the trick! Thank you!

I have just one follow-up question. I plan to put the nRF52832 and two I2C sensors (one of which is the MLX90393 mentioned above) on a custom PCB. Since I now know I need to put external pull-up resistors on the PCB, is 4.7kOhm still a good choice, or would it be a good idea to account for the resistance already there from the internal pull-up resistors that are configured to be active by the driver?

RE: TWIM not achieving 400 kbps

Håkon Alseth — Fri, 11 Jun 2021 06:38:57 GMT

Hi,

Could you try with external pull-up resistors? 400 kHz usually requires around 4.7kOhm pull-ups, as the internal pull-ups are too weak for this mode.

Kind regards,

Håkon