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BQ76930 garbage value

Shreenidhi Patil
Expert 3936 points
Other Parts Discussed in Thread: BQ76930, BQ76940

One of my customer has come up with an issue regarding voltage values read from BQ76930 chip. They get  some garbage value as a voltage from BQ chip (although they  have CRC check).They are reading  around 0.046V in some cases when they are trying to read cell voltage.

I asked them if they are following the timings given in the datasheet  properly before reading the next cell

They say they are using almost 2 sec delay before trying to read any new cell value

They say this issue occurs only sometimes , not always

Especially when they are starting up the system or when the I2C communication is broken and gets reestablished

They are using 2 BQ76930  chips to monitor total 20 cells

I am not able to understand how they are doing this though, As grounds will be different for both the chips

Can you please help me with this issue

 

is there any possibility that they are trying to read voltages at the same time BQ is trying to update its voltage value within registers by erasing it first ?

Or is there some other reason? If yes, how can we eliminate it?

 

  • 0
    Prodigy 90 points

    Shreenidhi,

    I am seeing something similar using a single BQ76940 with 12 cells. The first reading on power up after enabling the ADC/CC and seeing an alert w/ the "new CC measurement ready" bit set has some bad data.

    • we're using a chip with CRC, and the read data checks out.
    • cells 7&9 read as 0 raw (~46mV offset when converted, similar to your customer's wrong value)
    • external thermistors 2&3 also read 0 raw
    • on the next alert + read, these values are correct.

    Setup of the chip occurs ~20ms after startup. The datasheet says 10ms for everything to be ready after boot up, so we're enforcing 2x delay before configuring and turning on the ADC/CC just to be safe.

    When I insert some debug prints and delay that to ~40ms, the first reading is good.

    Did you ever resolve this issue for your customers?

    Thanks,

    Barrett