BQ76942: Can't Establish any I2C Communication With Chip

Ryan Coleman

Part Number: BQ76942

Hello,

My team is using a BQ76942 to control a 4Cell pack. An STM32G4 interfaces with the chip via I2C. We've created what seems like a fairly standard implementation of the chip using the reference design and have done a run of prototype boards but cannot establish I2C communication. We're using the STM32 example driver provided by TI.

We have TS2 pulled low and RST_SHUT is driven high by the MCU before attempting communication.

The MCU seems to be sending the address of the device 0X10 correctly but does not receive an Ack bit. Here is a screenshot of our logic analyzer looking at I2C.

What could be causing this issue?

Here is our schematic:

10 months ago

0 Ryan Coleman 10 months ago

Prodigy 25 points

Here is a screenshot of the signals on a scope.

0 Ryan Coleman 10 months ago

Prodigy 25 points

Could someone from Ti help us out with this? Thanks

0 Maxwell Verboncoeur 10 months ago in reply to Ryan Coleman

TI__Genius 16010 points

Hi Ryan,

This sounds like you're entering a soft-shutdown state. If the device attempts to enter shutdown mode while the TS2 pin is held low, the device will get stuck in a state of waiting to shutdown and the communications will be disabled.

To rectify this, TS2 should only be pulled low when waking the part from shutdown, and then released (floating) when the device has transitioned to normal mode.

You can read more about soft-shutdown at the end of Section 7.5: SHUTDOWN Mode of the TRM.

Regards,

Max Verboncoeur

0 Ryan Coleman 10 months ago in reply to Maxwell Verboncoeur

Prodigy 25 points

Can I leave that pin floating to debug it on our board?

0 Maxwell Verboncoeur 10 months ago in reply to Ryan Coleman

TI__Genius 16010 points

Hi Ryan,

Yes, the pin is meant to be left floating during normal operation when using the SHUTDOWN functionality. It would then be pulled down to wake the device from SHUTDOWN mode, and then released (floating) once the device has transitioned to NORMAL mode. This is explained in more depth in Section 7.5 of the TRM.

Regards,

Max Verboncoeur

0 Ryan Coleman 9 months ago in reply to Maxwell Verboncoeur

Prodigy 25 points

It's still not providing an ack bit. Even when that pin is left floating. Any more ideas?

Ryan

0 Maxwell Verboncoeur 9 months ago in reply to Ryan Coleman

TI__Genius 16010 points

Hi Ryan,

Looking at the table below from the datasheet, it may be that the device defaults to SPI communications, which would need to be changed in the OTP if you want the default to be I2C. Could you confirm which version of the BQ76942 you are working with?

Regards,

Max Verboncoeur

0 Ryan Coleman 9 months ago in reply to Maxwell Verboncoeur

Prodigy 25 points

It looks like I had to toggle the TS2 pin high then low at startup. This allowed us to communicate with the chip. Thanks

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BQ76942: Can't Establish any I2C Communication With Chip