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BQ34Z100-R2: ISOLATED I2C

Hal Mas
Prodigy 220 points
Part Number: BQ34Z100-R2
Other Parts Discussed in Thread: EV2400, BQ34Z100-DEVICE-FW, BQSTUDIO, ISO1541

Hey all,

Our battery setup includes a 9S LIPO battery, 2x BQ7790522PWR protectors, and the BQ34Z100PWR-R2 as our fuel gauge. We've added an isolator to ensure proper I2C communication for SDA and SCL due to the low-side circuit opening by the BQ7790522PWR.

However, I'm facing issues communicating with the BQ34Z100PWR-R2 using the EV2400. Our circuit has an external 5V input, regulated to 3.3V, and isolated to 5V_ISO, all confirmed with a multimeter.

Presently, I've connected PACK+ and GND to a 30V power supply. The measurements indicate 4V on REGIN and 2.5V on REG25, which appears within the expected voltages.

Regarding software, I've downloaded BQSTUDIO-STABLE. Despite not finding my exact part number, BQ34Z100PWR-R2, I've attempted using the closest matches available, such as BQ34Z100G1. Additionally, I obtained the BQ34Z100-DEVICE-FW and placed the file 0100_2_02-bq34z100.bqz in the config folder of BQStudio. Could anyone confirm if this is the correct approach?

Then what should be the correct selected files, 0100_0_16-BQ34Z100G1 or 0100_2_02-bq34z100 ?

When everything is plugged, it does not detect the device:

I removed the isolator U13 and the two PU R49 and R40 and I was able to communicate with the device:

The isolator used is the ISO1541QDRQ1 dedicated for I2C, isolated unidirectional clock, do you see any problem with that?

I looked at the I2C signals with the osclloscope, when I bypass the isolator, everything look good I see messages going:

With the isolator, I do not see the right stuff:

BQStudio says the device did not acknowledge.I tried changing the PU values to 1k, did not changed anything. I tried also to change the VCC2 (isolator) and PU to REGIN instead of 5V_ISO but it did worked better.

I am kind of stuck right now if you have any idea.

Thank you

EFuelGauge.pdfBatteryProtector.pdf

  • 0
    TI__Mastermind 18250 points

    Hi Hal,

    Yes, that was the correct the approach to downloading the DEVICE-FW, you can use 0100_2_02-bq34z100 from now on.

    When you remove the isolators and the I2C signal from the first screenshot was sent you could then communicate with the device on bqstudio?

    Regards,

    Evan

  • 0 in reply to Diego
    Prodigy 220 points

    Hi Evan, yes if I remove the isolator I am able to communicate with the chip.

    Do you think having 5v pull-up on the bq34 can be problematic, the chip is powered using the 4V from REGIN

  • 0 in reply to Hal Mas
    TI__Mastermind 18250 points

    Hi Hal,

    To clarify the distorted I2C oscilloscope screenshot was taken after the message passed through the isolator?

    Regards,

    Evan

  • 0 in reply to Diego
    Prodigy 220 points

    That is correct yes

  • 0 in reply to Hal Mas
    TI__Mastermind 18250 points

    Hi Hal,

    I believe your issue is not related to the gauge but rather the isolator.

    I am looping in someone from the isolator team to help.

    Regards,

    Evan

  • 0 in reply to Diego
    TI__Mastermind 22235 points

    Hello Hal, 

    Isolation team here, I understand that you are trying to use ISO1541 to isolate I2C signals. Have you gotten the design to work when VCC2 and the Pull-up are connected to the REG25 rail? Also, what is the maximum data rate of the I2C bus?

    Otherwise, I would like to mention that side 1 and side 2 of the isolator have different capacitive load capabilities. Side 1 is meant to be connected directly to the microcontroller (low capacitive loading) and side 2 is designed to be connected to the I2C bus (high loading). 

    In general, I2C devices are best suited for communication between devices on the same PCB and my experience issues when communicating off board or through and external connector.

    I hope this helps. 

    Best,
    Andrew