External pull-ups for I2C to achieve 5V

Hello,

Is the same true for the TM4C123GH6PM? We have an issue where the SCL pin (PA6) for one of the I2C modules is always low. Using the same code on an identical board works fine, so we seem to have damaged the SCL pin. We have the SCL and SDA lines pulled up to 5V. Could this be the reason for the damaged SCL pin?

Thanks,
Joe

Hi Amit,

As outsider I've little knowledge of your MCU's, "Switch-over" mechanism - between I2C & GPIO.

I can report - that on (some) MCUs - we have observed the "GPIO - appear to work" - yet the alternate function (I2C) did not.    Thus - somewhere in the MCUs internal routing/signal train - the alternate function "mechanism" (and it alone) appeared to have been damaged.

For a "factory fresh" (i.e. unstressed) MCU - the suggestion of switching to GPIO to confirm input/output capability - makes total sense.   (and serves to confirm that the user is probing or connecting to the correct pin)

When the pin becomes "ill behaved" such "GPIO to confirm" bets may be (bit) off...

Hi,

I'll try toggling it tomorrow and let you know the result.

Also, I have posted this issue as a new thread, so we should probably reply there. My apologies for this: after I posted to this thread, it occurred to me that since I have a different processor a new thread may be more appropriate. Sorry for any confusion. The new thread is called "TM4C123 using I2C: pulling SCL/SDA to 5V a problem?"

Joe

Hi Amit,

To follow up on this post:

Amit Ashara said:

Hello Tianlei,

I2C SCL cannot be configured as open drain as the Open Drain control is handled by the I2C Controller. You can have an external or internal Pull Up. However to be noted here is that TM4C129 does not have 5V tolerant IO's. So connecting a Pull up to 5V would not be a recommended solution.

Regards
Amit

if the TM4C129 pin is not I2C, but rather only used as an open drain digital output, can it be pulled up to 5V? I see references throughout the design guidelines and datasheet for the TM4C1294NCZAD that state its max GPIO input voltage is 4V, and that TM4C129 pins are configured as inputs they are 3.3V-tolerant, not 5V-tolerant. However, it is not clear to me whether this is also the case when the pin is configured as an open drain output.

If it is acceptable to drive a TM4C129 pin as an open drain output pulled up to 5V, is there a similar document to SPMA053 as a design guideline? SPMA053 nicely details the leakage current source to ground  when the output is set to open drain, for correct sizing of the pull-up resistor.

And finally, even if it were acceptable to drive an open drain output to 5V on the device, is there any input voltage clamping that would skew the voltage / current relationship?

Thank you in advance for your response.