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BQ4050: SMBus clock pull down problem

Brian Mulder
Prodigy 40 points

Part Number: BQ4050
Other Parts Discussed in Thread: BQSTUDIO, BQ40Z50

HI ... got a strange problem.

When I communicate to the BQ4050 via SMBus, the first byte 0x16 gets acknowledged.  Thats good.  Second byte 0x44 results in the BQ4050 pulling the  clock line low when requesting acknowledge.  It clamps this line for about 500uS.  

If I send a 0x00 instead of 0x44, same result, except the 500uS is reduce to 100us.   

I am struggling to get the chip working in a 4S configuration. Documentation for this chip is really bad.    From what I can determine, under no conditions does the BQ4050 pull the clock line low.

Anybody provide clues as to the above result.

  • 0
    TI__Guru 52115 points

    I would suggest you use the Advanced Comm SMB Window in the bqStudio to communicate with the bq4050 device and share with us some scope captures if you can see the same issue.

    Andy

  • 0 in reply to Andy Liu (BMS)
    Prodigy 40 points

    Hi Andy

    No references to bqstudio please.    My board has a 8 bit CPU controlling various things and communicating via SMBus protocol to BQ4050.  No studio, no dev board ... just basic commands is all I need.    Circuitry copied from a TI USB C board.   Every datasheet for anything relating to I2c or SMbus typically have waveforms showing how to communicate.  The BQ4050 datasheet does not even list the 0x16 device address.

    Andy, need data relating to what needs to be sent to device.   The  sluuaq3 document details that I must send 0x44 .. then data.  Just following that example and getting the results as mentioned.  If I scope this chip, I am seeing pulse wave forms on the temp sensor inputs.

    Something else that is bothering me .. the N channel FET control is in positive supply line ... and therefore will require a boost voltage to drive the fet gates.  The BQ4050 does not have any boost capacitor or output to confirm this voltage even exists. Datasheet once again very confusing on what I should see.   

    Thank you ..Brian

  • 0 in reply to Brian Mulder
    TI__Guru 52115 points

    The BQ4050 needs to configured correctly before it can work as expected. Believe me, it is not something that can be simply handled by your 8-bit CPU.

    One major step is to set the CEDV Parameters. Also, you would need to do the calibration before you start to collect data. If you don't have the proper tool (like bqStudio), you will see much trouble.

    See the following thread about how to use the bq40z50.
    e2e.ti.com/.../823717

    Andy