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BQ24031: How many volts does the internal system start to operate correctly?

user1866475
Intellectual 350 points
Part Number: BQ24031
Other Parts Discussed in Thread: BQ25180

Hi all,

How many volts does the internal system start to operate correctly?

The recommended operating conditions in the datasheet say 4.35V~. However, when I tried it, if the input voltage is above the battery voltage, it will start charging.

For example, if USB charging is set to 500mA and a 100mA USB charger is connected to the USB input and no AC input, its USB voltage will be lower (For a USB adapter with a supply capacity of 100 mA, 500 mA of charging current is a lot, causing a voltage drop). If it is less than 4.35V, will the BQ24031 not be able to control charging correctly and will have dangerous charging behavior?

I don't think so; 4.35V is the voltage needed to complete the charge, and I think the controls inside the BQ24031 are working correctly at the lower voltage.

If so, please let me know how much voltage is required at which pins for the BQ24031 to operate correctly? 

If charging with a low input voltage, which I used as an example, is dangerous, then I need to detect the input voltage and not charge. Because I cannot develop a product without countermeasures with just a simple warning, putting the responsibility for that danger on the user.

Best Regards,

Yukio Oyama

  • 0
    TI__Mastermind 23200 points

    Hi Yukio,

    You're correct that 4.35 V is the voltage needed to properly charge the battery to the regulation voltage but it can start charging when the device exits sleep mode.

    If it is less than 4.35 V, the device may not be able to regulate charge correctly as the battery voltage increases. As this is a linear charger, it requires that the OUT pin voltage have sufficient headroom to charge the battery to the battery regulation voltage. This requires that VIN to be above the battery regulation voltage with headroom. This leads to 4.35 V for propery battery charging and other operations. Outside of this, you may run into loops such as DPPM or even supplement mode. 

    You will need to define what is dangerous in terms of your product operation. Is it input voltage collapse? Is it not charging? Is it not battery termination? 

    If you'd more information from the charger for operation, I highly recommend the BQ25180 for up to 1A charging. It's an I2C device and you'll be able to monitor numerous items about the charger operation to be able to perform items such as input quality and control loops. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Intellectual 350 points

    Hello Anthony-san,

    Thanks for your response and your BQ25180 suggestion. I want to do the charging even before the host cpu boots up. I can't monitor the I2C all the time so using the BQ25180 would not solve my problem.

    What I mentioned in my example is the problem I am facing. When using a USB adapter with insufficient supply capacity, the USB voltage falls below 4.35V.

    But it balances at a point about 0.1V higher than the battery voltage. And as the battery voltage rises due to charging, the USB voltage also rises. Finally, the CV mode reduces the current, the USB voltage becomes normal, and charging is completed.

    My concern is whether the temperature detection and timer functions will still work correctly when the voltage is below 4.35V and whether the DPPM will work correctly.

    Best Regards,

    Yukio Oyama

  • +1 in reply to user1866475
    TI__Mastermind 23200 points

    Hi Yukio-san,

    Ah I understand a bit better now. 

    Whenever the charger current is reduced due to a regulation loop such as DPPM, it will slow down in the same amount that charger current is reduced. So if the charge current has reduced by 50%, the clock will slow down by 50%. 

    Temperature function should not be affected. 

    Let me know if there are any other concerns!

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Intellectual 350 points

    Hello Anthony-san,

    Thanks for your response.

    I understood that the temperature function is not affected and that the timer period gets longer as the charging current decreases.
    Finally, I am checking again. Does your answer hold true while charging below 4.35V, which is the premise of my question?

    Best Regards,

    Yukio Oyama

  • 0 in reply to user1866475
    TI__Mastermind 23200 points

    Hi Yukio-san,

    As you mentioned, the 4.35 V is part of our recommended operating conditions. When operating outside of these conditions, you may see behaviors such as DPPM, a common result from a collapsing VIN. I have mentioned that charging can start lower than 4.35 V and mentioned how the device is affected when charging below 4.35 V. I have also mentioned that any regulation loop that reduces the charge current will affect the timer. This could be a regulation loop such as DPPM that can occur because of a low VIN.  The temperature function is not affected. 

    If you are still operating below 4.35 V when the battery is in CV, you will not see termination if the device is operating in DPPM

    For any charging to occur, your VIN needs to be above VBAT with enough headroom, which you've observed. This is within the operations of the device. 

    In short, yes, my answer still holds true while charging below 4.35 V. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Intellectual 350 points

    Hello Anthony-san,

    Yes, under my conditions VIN is well above 4.35V when charging reaches CV mode. There is enough headroom for the device to finish charging.

    I am relieved to know that the charge protection works correctly even below 4.35V. I 'll design carefully about the timer period  varies.

    That's all for my questions. Thanks for your support, I appreciate it. I'll close this case, thank you.

    Yukio Oyama