TXS0102: I2C SCL not pulled low

Jose Xavier

Part Number: TXS0102

Hi,

I used an TXS0102 to interface a GPS device with logic voltage at 2.8V with an host uC at 3.3V. I2C clock signal is ok and the 2.8V converted signal is also ok however I2C data line is not pulled low and that only happens if I have the TXS0102 connected. If I cut the connection between the host ic and the TXS0102 it is pulled low.

Is there anything that doesn't look correct on the schematic?

Thank you

over 1 year ago

0 Jack Guan over 1 year ago

TI__Mastermind 27011 points

Hi Jose,

This is seen in cases where there is an external pullup resistor to the TXS0102. Note that the TXS family has internal 10kohm pullups already, so external pullups are not needed. I do not see any in the schematic, but can you confirm if there are any internal to the host/ peripheral? If possible, please also provide waveforms of the anomaly seen.

Regards,

Jack

0 Jose Xavier over 1 year ago in reply to Jack Guan

Prodigy 10 points

I forget to post the picture of the waves. The host IC has the pins configured for I2C as usually. I will have to check if it is has any pull up internally turned on.

0 Jack Guan over 1 year ago in reply to Jose Xavier

TI__Mastermind 27011 points

Hi Jose,

Thanks for sending the waveforms. Please reach out once it is determined that the pullups do/ do not exist.

Here is an app note that discusses how the external pullups effect the internal pullups (leads to voltage divider network):

Effects of pullup and pulldown resistors on TXS and TXB devices

Regards,

Jack

0 Jose Xavier over 1 year ago in reply to Jack Guan

Prodigy 10 points

The I2C slave device is a GPS and to be able to use I2C I need a different firmware version. Updated the GPS firmware and I2C is now working.

Thank you

+1 Jack Guan over 1 year ago in reply to Jose Xavier

TI__Mastermind 27011 points

Hey Jose,

Can you confirm if updating firmware resolved your issue? If so, I will close this thread.

Regards,

Jack

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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TXS0102: I2C SCL not pulled low