BQ34Z100: SCL getting held low on I2C

Darren Jenkins

Part Number: BQ34Z100

Tool/software:

Gauge team,

Our customer is working with BQ34Z100 in a battery pack. The fuel gauge pulls the clock line low indefinitely and the only way to get it to release is a power cycle of the gauge.

The clock is running at 100kHz.

First, can you confirm if this gauge implements clock stretching? I don't see it in the datasheet, while it is mentioned in the datasheet of other gauges. Like here:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1383921/bq27z561-r2-i2c-clock-stretching

Second, do you know why the gauge might be holding the clock low? Have you seen this before?

Note, I believe they built these packs with BQ34Z100, not BQ34Z100-R2. I'm not sure if this is a factor.

Thanks,
Darren

over 1 year ago

0 Diego over 1 year ago

TI__Mastermind 25795 points

Hi Darren,

Yes, the gauge supports clock stretching. It is listed in the TRM.

I have seen this problem before. Usually, customers have to fix this in software by cutting off power to the device.

Another solution that may work is to rapidly pulse the clock line and they may get the line unstuck.

Regards,

Diego

0 Darren Jenkins over 1 year ago in reply to Diego

TI__Genius 12461 points

Hi Diego,

What do you mean about fixing it in software by cutting off power? Can you explain specifically how that is done?

This is in a battery pack, so physically removing power to the gauge is very difficult.

Thanks,
Darren

+1 Diego over 1 year ago in reply to Darren Jenkins

TI__Mastermind 25795 points

Hi Darren,

The particular customers BMS has the capability to disconnect the gauge from the battery using external components controlled by the MCU.

You can pulse the clock line by the MCU rapidly this has been seen to unstick the clock lines.

This may also work but I cannot test it because I have never seen a device with this problem.

Please let me know if a solution is found,

Regards,

Diego

0 Jasen Higgins over 1 year ago in reply to Diego

Prodigy 20 points

Hi Diego / Darren,

We also ran across the note in the datasheet about holding the SCL / SDA lines low for >= 2 seconds and tested that today. It worked as advertised and the pack has been restored without needing to cycle power.

Thanks for following up!

Jasen

0 Adrian over 1 year ago in reply to Jasen Higgins

TI__Mastermind 37761 points

Hello,

Today is a national holiday. We will get back to you later this week.

Regards,

BMS Apps Team

0 Diego over 1 year ago in reply to Adrian

TI__Mastermind 25795 points

Hi Jasen,

Glad a solution was found!

Regards,

Diego

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BQ34Z100: SCL getting held low on I2C