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BQ25700AEVM-732: Charge Current Resister setting value changed

vel murugan
Intellectual 380 points
Part Number: BQ25700AEVM-732
Other Parts Discussed in Thread: BQ25700A

Hi Team,

I am using BA25700AEVM to Charge the smart Battery. I have a problem with Charger Current resistor settings. And I have set the charge current value to 1024 mA. But that resistor value automatically changed to near 2A 

I'm Stucked with this problem I don't understand the what i am missing.

Used following below setting:

1) ChargeOption0 resistor value is 0x020E.

2) ChargeCurrent resistor value is 0x400;

and read the value from smart battery resistors.

  • 0
    TI__Genius 10240 points
    Vel,

    I think you mean "register" instead of "resistor". You might want to check whether the smart battery commanded 2A charging current. BQ25700A does not change the ChargeCurrent register setting.
  • 0 in reply to ezhao
    Intellectual 380 points

    Hi Eric,

    thanks for your reply.

    Yes I mean register.  Yes I am monitoring the Charging current but it was changed to 2A. 

    Now i m mention the following steps:

    1) Set the MaxChargeVoltage is 0x4140. // 16.704 Volts

    2) Set the ChargeCurrent is 0x0400.  // 1 Amps charge current

    3) Set the ChargeOption0 is 0x020E.

    while loop:

    if charging:

    1) Read the charger current value from battery and charger.

    Here i set a  break point and check the value of charge current, that value was changed to 2A in Charger and battery.

    If I set the charge current to 1A inside the while loop before reading the current value from charger, I always get 1A while reading. But if I set the charge current value as 1A only once i.e. before the while loop, then after sometime I get an output of 2A irrespective of any charge current value set before.

  • 0 in reply to vel murugan
    TI__Mastermind 25800 points
    Hey vel,

    Can you confirm the I2C datasheet being sent inside and outside the while loop is being sent correctly?

    Do you see the same problem if you remove your Smart battery from SMBus lines without removing power?


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 380 points

    Hi Joel,

    Can you confirm the I2C datasheet being sent inside and outside the while loop is being sent correctly? 

    I wanted to check whether  charge current setting is to be set only once (Outside While loop) or each time when we write (Inside while loop).

     

    Do you see the same problem if you remove your Smart battery from SMBus lines without removing power? 

    No, on removing the smart battery while running the charge function the current setting was not changed, but when connecting battery the charge current register setting was changed to 2 A immediately.

     

    Is there any time constraint / Time out that needs to be addressed while writing into a register of charger IC??

  • 0 in reply to vel murugan
    TI__Mastermind 25800 points
    Hey vel,

    It should only need to be written once. 2A is not a default state. There are cases where the charge current will reset back to 0mA or change be set to 128mA, but not 2A.

    If you plug in the battery without attaching the SMBus lines, do you also see the same behavior. You mentioned last time you removed the entire battery. But I want to check when you connect the battery without the communication lines connecting to the rest of the SMBus.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 380 points

    Hi Joel,

    Thanks for your clarification.

    If you plug in the battery without attaching the SMBus lines, do you also see the same behavior. You mentioned last time you removed the entire battery. But I want to check when you connect the battery without the communication lines connecting to the rest of the SMBus.


    As you suggested, during charging we have removed  SMBus lines alone from battery (keeping the battery Supply+ & Supply-), charger current register value did not change. But when connecting battery SMBus lines, the charge current register setting was changed to 2 A immediately.

     

    Regards,

    vel

     

  • 0 in reply to vel murugan
    TI__Mastermind 25800 points
    Hey vel,

    To me, it sounds like the Smart Battery is writing something to the SMBus lines that be toggling. Can you check the SMBus lines when the battery pack is applied? I want to see what communication is occurring on the SMBus lines, preferably with a Logic Analyzer.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 380 points

    Hi Joel,

    thanks for your help.

    The smart battery was writing the charger current and voltage to smart charger. (i.e) the current value was changed.

    Please, find that screenshot of the datasheet reference below.

    will it change because of what is mentioned above?

  • 0 in reply to vel murugan
    TI__Mastermind 25800 points
    Hey vel,

    The SMBus address of the charger is 0x12 so it is entirely possible the smart battery is writing to the I2C register of the charger and reprogramming the voltage and current settings.

    You should ask you smart battery pack vendor to describe the operation of the ChargingVoltage() and ChargingCurrent() broadcasts. We can only identify items on the charging side and cannot comment on the battery pack side.


    Regards,
    Joel H