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BQ25120A: Minimal hardware pin requirement for full control of chip

agusta mir
Intellectual 480 points
Part Number: BQ25120A


Hi,

I am currently evaluating the part BQ25120A for use in a low power system where the host uC controls the chip(to power itself and other peripherals). I don't have the liberty to use extra i/o lines for this chip than the shared I2C bus. I have looked through the datasheet, and I wanted to confirm if the chip can be fully operated using the I2C interface. Part of my use case is to control charging (en/dis and current), control the LDO (en/dis and voltage level). I plan to not use INT, /RESET, LSCTRL directly but control and monitor their status from the I2C interface. I am unclear on how to use the CD pin. It looks like it is required to enable I2C transactions and also for charging. What should be it's configuration if it is not going to be controlled via a hardware pin?

  • 0
    TI__Genius 10385 points

    Agusta,

    From what you mentioned, in I2C you are able to control:

    - Enable/Disable charging - REG03[1]

    - Enable/disable LS/LDO - REG07[7]

    - Set LDO voltage - REG07[6:2]

    - Enable/disable INT function REG02[3]

    You will have to pull /CD, /RESET, and LSCTRL high to be able to use the device as you are describing.

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Intellectual 480 points

    Ricardo,

    Thanks for the answer. On the eval kit, I have the a 5V input and a battery connected. The jumper for CD pin connected to VSYS allows to enable charging (status reads charge Ready), but I have to remove the jumper for the status to change to "charge in progress". If we pull CD to high as is on the eval kit, how will charging work?

  • 0
    TI__Mastermind 21590 points

    Hello Agusta,

    What changes do you anticipate making with your software through I2C on this device? The only pin that might need to be changed will be the /CD pin. When VIN is present and /CD is low, charging is enabled however when VIN is absent and /CD is low, the device will go into Hi-Z mode. In Hi-z mode, the device will be on a lower Iq state but there will be no I2C communication. If you don't anticipate any I2C changed in BAT only mode, you can just leave /CD low the entire time and not need any GPIOs

  • 0 in reply to Raheem
    Intellectual 480 points

    Hi Raheem,

    My use case is to

    - Adjust VSYS level, control the LDO (en/dis and voltage level) via I2C. This operation will be carried out in absence of Vin.

    - Control charging (en/dis and current). This will be in presence of Vin.

    Vin is not expected to be present at all times when I2C transactions need to be carried out, as the system is expected to be powered via battery. 

    Given this scenario (I2C transaction with battery powered operation), and from you answer,  it seems that at the very least the CD pin needs to be connected to the host? 

  • 0 in reply to agusta mir
    TI__Mastermind 21590 points

    Hello Agusta,

    You'll need at least  one i/o for the /CD pin for control when in BAT only mode to allow I2C transaction.

  • 0 in reply to Raheem
    Intellectual 480 points

    Hi Raheem, 

    thanks for the answer. Can you please clarify, you mentioned the following:

    "When VIN is present and /CD is low, charging is enabled however when VIN is absent and /CD is low, the device will go into Hi-Z mode. In Hi-z mode, the device will be on a lower Iq state but there will be no I2C communication."

    I am looking at the state diagram from the datasheet, and it seems to be contrary (also to observed behavior). How to interpret this diagram correctly?

    Another follow-up question: The difference between highz and active battery is that the i2c interface is off in high z. Other outputs such as sys, ldo outputs are not affected in high-z mode?

  • 0 in reply to agusta mir
    TI__Mastermind 21590 points

    Hello,

    The state diagram is correct. You'll see the arrow goes into Hi-Z mode when /CD is high and the arrow points to leaving Hi-Z mode when /CD is low and VIn is present.

    For  the second question, you're correct.

  • 0 in reply to Raheem
    Intellectual 480 points

    Allow me to follow up on the state diagram. I am unclear about why the transition from high-z to active battery happening when /CD is low and Vin being absent. Does it not contradict Table 1 (CD state table) ? 

  • 0 in reply to agusta mir
    TI__Mastermind 21590 points

    Hello,

    If you take a look at the diagram, you'll not that it says "CD" and not "/CD".