TPS65988: I2C lines during power-on

Diego Lewis

Part Number: TPS65988

Hi Team,

My customer is seeing a droop on their I2C line connected to the TPS65988 while powering on the device (see image below, green is the I2C communication, red is the 3.3V PD controller supply, ignore other two lines). It looks like the PD I2C bus is getting released before it has reached 3.3V, and they are concerned that this drop could cause an undesired low bit.

Do we have any recommendations to help prevent this from happening?

Regards, Diego Lewis

over 6 years ago

0 Eric Beljaars over 6 years ago

TI__Mastermind 36756 points

Hi Diego,

It looks like they are reading/writing to the TPS65988 before the device has fully booted. If the red line is indicating VIN_3V3 then the device has not yet booted when they start I2C transactions. Please ensure that the I2C pull-up lines are pulled up to LDO_3V3 from the PD controller.

Thanks,
Eric

0 Diego Lewis over 6 years ago in reply to Eric Beljaars

TI__Intellectual 1540 points

Hi Eric,

They are not attempting to communicate with the TPS65988, but there are other devices talking on the same line. Since they don't care about dead batteries in this application they are using the pull-ups on their 3.3V system rail, not the LDO rail.

Regards, Diego Lewis

0 Eric Beljaars over 6 years ago in reply to Diego Lewis

TI__Mastermind 36756 points

Hi Diego,

I'm not sure if the TPS65988 is what could be causing this. During Reset (or boot up), the I2C lines are in a High-Z state so they should not be interfering with the I2C signals at all.

Thanks,
Eric

0 Diego Lewis over 6 years ago in reply to Eric Beljaars

TI__Intellectual 1540 points

Hi Eric,

Understood. However, based on the capture above my customer is concerned that the device is exiting high-Z too early.

Regards, Diego Lewis

0 Eric Beljaars over 6 years ago in reply to Diego Lewis

TI__Mastermind 36756 points

Hi Diego,

I have not been able to reproduce this on the EVM. Can you check to see if the 3.3V system rail is exhibiting this same behavior?

Thanks,
Eric

0 Diego Lewis over 6 years ago in reply to Eric Beljaars

TI__Intellectual 1540 points

Hi Eric,

My customer is using the 3.3V system rail to pull-up the I2C lines since they have multiple devices on the same bus.

Regards, Diego Lewis

0 Eric Beljaars over 6 years ago in reply to Diego Lewis

TI__Mastermind 36756 points

Hi Diego,

I would suggest working with the customer to see if the problem can be isolated further. I don't think this issue is related to the TPS65988.

Thanks,
Eric

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TPS65988: I2C lines during power-on