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BQ77PL900 IIC to stm32

user46172831
Prodigy 60 points
Other Parts Discussed in Thread: BQ77PL900

Hi,

 I'm using BQ77PL900 to monitor six batterries. The host is STM32F407. I have some questions to ask:

1.If the BQ77PL900 is in the mode of UNDERVOLTAGE, is the IIC conmunication normal.

2. Now,the 5V and 3.3V LDO of the BQ77PL900 in my board  is normal, but when the host communicate with BQ77PL900, the host can't recieve the ack. Could you help me solve the problem?

  • 0
    TI__Guru 54715 points
    1. If the part is in host mode when it goes to UNDERVOLTAGE, I2C will remain normal. If the part is in standalone mode when it goes to UNDERVOLTAGE and there is no voltage on PACK it will shut down.
    2. Be sure the part has the correct VLOG connected for the interface level. After that it should be like any other I2C diagnostic.
    Inspect the signals with an oscilloscope and see if signal quality is good. Compare to a working board or working condition. If there is no other working bq77PL900, compare the signal quality with another I2C slave with a simple register interface which the host can address. If you have included series ESD resistances like the EVM be sure the values are as intended and that the signal can go low on the other side based on the driving source. Be sure START is sent and check the address on the bus. ACKing a start and the device address is the most basic function of the slave interface.
  • 0
    Prodigy 60 points
    Thank you

    在2016-05-03 22:25:51，20144009@stu.neu.edu.cn写道：

     

    A Message from the TI E2E™ Community
    Texas Instruments

     

    WM5295 replied to BQ77PL900 IIC to stm32.

    1. If the part is in host mode when it goes to UNDERVOLTAGE, I2C will remain normal. If the part is in standalone mode when it goes to UNDERVOLTAGE and there is no voltage on PACK it will shut down.
    2. Be sure the part has the correct VLOG connected for the interface level. After that it should be like any other I2C diagnostic.
    Inspect the signals with an oscilloscope and see if signal quality is good. Compare to a working board or working condition. If there is no other working bq77PL900, compare the signal quality with another I2C slave with a simple register interface which the host can address. If you have included series ESD resistances like the EVM be sure the values are as intended and that the signal can go low on the other side based on the driving source. Be sure START is sent and check the address on the bus. ACKing a start and the device address is the most basic function of the slave interface.

     
     

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  • 0
    Prodigy 60 points
    Hi:
    The problem I asked you for help last time have been solved. But the new problem comes. The new problem is about current monitor. When no load, I test IOUT is 1.221V, which is not 1.2V. The problem cause  I couldn't use the formula: VCURR = 1.2 + (IPACK × RSENSE) × (IGAIN) to caculate the current. Do you think how can I solve the problem?
    Thank you.

    在2016-05-04 22:15:54，20144009@stu.neu.edu.cn写道：

     

    A Message from the TI E2E™ Community
    Texas Instruments

     

    user46172831 replied to BQ77PL900 IIC to stm32.

    Thank you

    在2016-05-03 22:25:51，20144009@stu.neu.edu.cn写道：

     

    A Message from the TI E2E™ Community
    Texas Instruments

     

    WM5295 replied to BQ77PL900 IIC to stm32.

    1. If the part is in host mode when it goes to UNDERVOLTAGE, I2C will remain normal. If the part is in standalone mode when it goes to UNDERVOLTAGE and there is no voltage on PACK it will shut down.
    2. Be sure the part has the correct VLOG connected for the interface level. After that it should be like any other I2C diagnostic.
    Inspect the signals with an oscilloscope and see if signal quality is good. Compare to a working board or working condition. If there is no other working bq77PL900, compare the signal quality with another I2C slave with a simple register interface which the host can address. If you have included series ESD resistances like the EVM be sure the values are as intended and that the signal can go low on the other side based on the driving source. Be sure START is sent and check the address on the bus. ACKing a start and the device address is the most basic function of the slave interface.

     
     

    You received this notification because you subscribed to the forum.  To unsubscribe from only this thread, go here.

    Flag this post as spam/abuse.



     
     

    You received this notification because you subscribed to the forum.  To unsubscribe from only this thread, go here.

    Flag this post as spam/abuse.



  • 0 in reply to WM5295
    Prodigy 60 points

    Hi:
    The problem I asked you for help last time have been solved. But the new problem comes. The new problem is about current monitor. When no load, I test IOUT is 1.221V, which is not 1.2V. The problem cause  I couldn't use the formula: VCURR = 1.2 + (IPACK × RSENSE) × (IGAIN) to caculate the current. Do you think how can I solve the problem?
    Thank you.

  • 0 in reply to user46172831
    TI__Guru 54715 points

    The 1.2V is a typical value, the actual value will vary with the individual part and conditions.  You can measure the reference voltage using IACAL as shown on page 33 of the datasheet.  Bias current from the sense inputs will have an effect on the reported value, those may be negligible if you have used small filter resistors.  However you may want to calibrate your system with zero current to get an offset.  You may also want to calibrate a current gain to accomodate variations in the IC gain and tolerances in the sense resistor and installation.

    The 1.221V seems like a reasonable variation from typical.  The internal references are described with a 2% tolerance, although those are expressed on the Vcell section rather than the VIOUT.  Note also the input offset voltage will affect the VIOUT.  If your zero current output becomes too far from 1.2V you will need to consider if the IC has been damaged or there may be an assembly defect.