ISO1640: Compatibility between cc13xx/cc26xx family and ISO1640/ISO1540

Hi Andreas,

Your understanding on V_OL1 of ISO1640 and ISO1540 is correct. This is a common industry practice for bidirectional I2C isolators. For more info, please go through the [FAQ] Why is the logic LOW level output voltage, VOL1, up to 0.8V on Side1 of the ISO1540/ISO1541 and ISO1640/ISO1641 bidirectional I2C isolators? . 

As you mentioned, the cc13xx/cc26xx family V_IL = 0.2 * V_DDS which at 3.3V_DDS is 0.66V. May I know the application and the I2C nodes on side 1 and side 2?
The V_OL2 will be 0.4V max, ISO1540 and ISO1640 can still be used with cc13xx/cc26xx.

Thanks
Vikas J

As discussed in private, you confirmed our usage of ISO1540/1640 is correct for our application with cc13xx/cc26xx on side 1.

One remaining question is the i2c logic levels on cc13xx/cc26xx. On an older post from a TI employee on i2c logic levels in general: "The VIH and VIL thresholds are defined on the I2C specification. On the latest revision of the spec, the thresholds are defined as follows: VIL=0.3*VDD, VIH=0.7*VDD". With 0.3 * VDD instead of 0.2, the ISO1540/1640 level would be ok. Is it possible that the cc13xx GPIO logic level (which I was quoting) is not the same as its I2C logic levels? (the datasheet only mention GPIO)

Old post: e2e.ti.com/.../bq25892-question-regarding-i2c

Vikas Jeevannavar would you mind assigning to the correct team?

Hi Andreas,

I am moving this post to the group responsible for cc13xx to help you with query on logic levels of cc1312R.

Thanks
Vikas J

Thanks for your help

Hi Andreas,

For CC1312R, VIL can be maximum 0.2VDDS and VIH can be minimum 0.8VDDS. If you use side 2 of ISO1640 with CC1312R, they will be compatible. Why are you not using side 2? Do you need it for the other device?

Best regards,

Haiatullah

Hi, yes I discussed our application privately with Vikas and he confirmed we need cc1312r on side 1.

Does this mean that the cc13xx/cc26xx family is not adhering to the i2c standard? Ref. the older post I linked above (https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/568290/bq25892-question-regarding-i2c) and the NXP I2C application note slide 29 (https://www.nxp.com/docs/en/application-note/AN10216.pdf) which specifies V_IL as 0.3 x VDD.

Friendly reminder Haiatullah Gholami, if you had any input on cc13xx/cc26xx and i2c compliance

Hi Andreas,

My apologies for the delayed answer. I was reaching out to our validations team for clarification on this matter. They are looking at this, and need some time to investigate it further. I will come back to you in a week to give you an update. Thank you for your patience! 

A possible solution to using ISO1640 with CC1312R is to use a 3.6 V supply for CC1312R. If you use a 3.6 V supply, VIL of CC1312R will be 0.2*3.6V=0.72V which is higher than the maximum VOL of ISO1640. Is this something that could work for you?

Regards,

Haiatullah

Thank you for the suggestion, unfortunately we cannot change the voltage at this point in our design.

That's great! Thanks for the quick update.