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BQ24773: Remove the adapter

Denny Huang
Expert 7170 points
Part Number: BQ24773
Other Parts Discussed in Thread: BQ25306, BQ25792, BQ25672

Dear team

Customer want to confirm if it is possible.

1. If the host IC doesn't connect to BQ24773 via I2C whether the charge ic enabe to execute charge?

2. If the status of host ic  is power-off whether the charge ic enabe to execute charge?

3. Is it possible to detect the adapter exist via I2C and notify to host ic? whether the host could detect powered by battery or adapter? 

4. How long about the switch time from adapter power off to battery.

Many thanks

Denny 

  • 0
    TI__Genius 11850 points

    Hi Denny,

     

    1) and 2) At POR, the ChargeCurrent() register setting is 0 mA. The host MCU must write to the registers in order to enable charging the battery.

    3) Unfortunately, the BQ24773 does not have a register which shows whether the adapter and battery are present or not. As an alternative solution, you can use the host MCU to monitor the ACDET voltage in order to determine whether the adapter is present.

    4) When the adapter is unplugged, the BATFET will turn on so that VBAT can maintain power to VSYS.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    TI__Expert 7170 points

    Dear Angle

    Customer  have two questions, could you help to reply.

    1. The ChargeCurrent() register setting is 0 mA. The host MCU must write to the registers in order to enable charging the battery.

    Only the 1st time need to be written, or it need to be written every time ? Since in our product, the charger & Host MCU may separated to 2 independent part for some scenario. We need to understand if the charger could work stand alone when no host MCU present.

    3. When the adapter is unplugged, the BATFET will turn on so that VBAT can maintain power to VSYS.

         Do you have the data for the time gap for the switch time ?

    Many thanks 

    Denny

  • 0 in reply to Denny Huang
    TI__Genius 11850 points

    Hi Denny,

     

    The ChargeCurrent() register is reset every time the adapter is removed. However, if only the host MCU is disconnected, then the existing register settings are preserved. For example, if the host MCU writes to the ChargeCurrent() register, and then the host MCU is disconnected while the adapter remains present, then the ChargeCurrent() register setting is preserved, and the BQ24773 can continue charging the battery.

     

    In my tests on a BQ24773 EVM, the transition from adapter power to battery power can occur very quickly, on the order of a few hundred us. Due to the capacitance on VSYS and the quick BATFET turn-on time, the transition from adapter power to battery power was not an issue in my tests. If a more precise time measurement is needed, then I suggest testing an EVM using your test setup, operating conditions, and load conditions.

     

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    TI__Expert 7170 points

    Hi Angelo

    Thanks for your information and great support.
    We still need your help on my rest 2 questions :

    4. The BAT pin (pin-17) has the function of sense the voltage of battery pack. Could this data ( voltage of battery pack) be sent to host MCU by interface ?
    5. Is there any pin which can be connected to LED for charging indicator ?

    Many thanks

    Denny

  • 0 in reply to Denny Huang
    TI__Genius 11850 points

    Hi Denny,

    4) Some of our other chargers have an integrated ADC that allows the host MCU to easily read the battery voltage through the charger IC, but unfortunately, the BQ24773 does not support this. In many applications, the BQ24773 is paired with a battery gauge IC, which can report conditions such as the battery voltage, current, and SoC (state of charge) to the host MCU.

    5) Unfortunately, the BQ24773 does not have a pin for this purpose either, but some of our other chargers have a STAT pin which can be used with an LED to indicate when the device is currently charging.

    What are your adapter voltage, battery charge voltage, and max charge current? If you provide some more information about your application requirements, I can let you know if there's a different charger IC which may be more suitable than the BQ24773.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    TI__Expert 7170 points

    Hi Angelo

    Thanks for your reply. The information as below.

     

    1. Adaptor Voltage : 12V
    2. Battery Charge voltage : we use 2 cell series structure, so 8.4V typ. (we hope charge voltage adjustable)
    3. Max charge current : <1A
    We may need to monitor the battery voltage, and control the LED for charging status indicator.

    Many thanks

    Denny

  • 0 in reply to Denny Huang
    TI__Mastermind 33255 points

    How about BQ25306 -- Standalone 17-V, 3A 1-2 cell buck battery charger?

    www.ti.com/.../BQ25306

  • 0 in reply to Tiger Zhou
    TI__Expert 7170 points

    Dear  Tiger

    thanks your recommend, could you suggest charging ic with I2c interface?

    many thanks

    Denny

  • +1 in reply to Denny Huang
    TI__Genius 11850 points

    Hi Denny,

     

    The BQ25792 can meet all of your requirements. It has an I2C interface and integrated ADC, so the host MCU can easily read VBAT through the charger. The BQ25792 also has a STAT pin to indicate the charging status. The switching FETs and BATFET are all integrated inside the IC, which simplifies the layout and reduces the BOM count.

     

    Alternatively, you can use the BQ25672. This device is very similar to the BQ25792, but it is only a buck charger, not a buck-boost charger. The BQ25672 and BQ25792 should both be better fits for your application compared to the BQ24773.

     

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    TI__Expert 7170 points

    Hi Angelo

    I appreciated your great support.

    Many thanks

    Denny