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BQ24295: Power management using bq24295

hafedh hamouda
Prodigy 130 points
Part Number: BQ24295

Hello,

I want to build management battery circuit which can deliver power to :

- The main system (3.3V)

- Battery (Li-Polymer, 1 cell, 2800 mAh, 3.7 V)

- External device via USB-A (5V - 1A max)

Several use cases must be taken into consideration : 

- When the adaptor mini-USB cable is plugged into the power bank, the charger initiates the D+D- detection to determine the input current capability and set the charger input current not to exceed the detected value. If the external device is attached to a Type-A USB terminal via cable, the adapter current will guarantee the bypass phone charging-only the remaining extra power will charge the battery.

- The power bank operating in boost mode, when the adapter is unplugged and the battery voltage is boosted to around 5V to charge the external device. 

- The main system should always be powered

The bq24295 is the best candidate, but I am would like to understand how this chip can switch to the boost mode when the adapter is removed. I want to control all mode without software control.

Thank you in advance for your feedback

  • 0
    TI__Mastermind 25800 points
    Hey Hafedh,

    Just to clarify one of the use cases:
    In the event the power bank's adapter is plugged in AND the external phone that needs charging is plugged in, the power bank (using the BQ24295) can only set the current limit based on D+/D- detection for its own charging current. This means it can only limit the current that flows to charge the power bank's battery. It cannot control the current flowing to charge the external phone connected to the Type-A port.

    If that is understood, then this charger is fairly easy to use. One note is that if you are not using software control, I recommend reviewing the datasheet Table 4. Charging Parameter Default Setting to make sure those settings work for your power bank.

    For OTG/boost mode for the power bank functionality, it is very simple to use. Just pull the OTG pin to logic HIGH (either VSYS or VBAT) and when the adapter is removed, after 30ms (typical), the OTG rail will automatically come up to regulation give a high enough battery voltage is present.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 130 points

    Dear Joel,

    Thank you for your feedback.

    I need to ask you further questions :

    - What about the case when the phone is not  connected to the Type-A port ? the bq24295 can detect the presence of the phone?

    - In the case to powered my main electronic system (+3.3 V). Should I connect it directely to the Pin Sys? or I need to add an external LDO?

    - In case my adapter is type-C USB. Can I use D+/D- detection?

    - Do you have any solution to control the battery level in real time?

    Thank you in advance for your support.

  • 0 in reply to hafedh hamouda
    TI__Mastermind 25800 points
    Hey Hafedh,

    It cannot detect the presence of a phone on the PMID output. You would need some current monitoring or some other signal to determine this.

    I would use an LDO as the SYS voltage will track with the battery voltage.

    USB-Type C is just a connector that is intended for use with USB3.1 and the USB PD specification. D+/D- detection follows USB2.0 and moreso, the BC1.2 Specification. With just the D+/D- detection on the charger, the charger will detect settings based on BC1.2, even if you have a Type-C connector. However, if you need any handshaking for USB PD or on the CC1/CC2 pins of the Type-C connector, this charger will not do that.

    What do you mean control the battery in real time? Are you asking about controlling the discharge current to isolate the battery from the system load?


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 130 points
    Dear Joel,

    Thank you for your feedback.

    Actually, I will use the USB-C connected to Vbus pin. The pin D+/D- will be shorted and the current limit will be controlled via the resistor in the pin ILIM. (Is this correct?)

    Further questions :

    - I didn't understand how can I configure the bq24295 to switch in the shipping mode. Could you please help me to build this functionality?

    - In the case when the USB-C is unplugged, USB-A for external device also is unplugged and no load in the Pin SYS => In this case the battery is in shipping mode?

    - Do I need to add a reverse polarity protection? Overcurrent/Overvoltage protection? The bq24295 do not include an internal protection?

    Thank you in advance for you help

    Best regards

    Hafedh
  • 0 in reply to hafedh hamouda
    TI__Mastermind 25800 points
    Hey Hafedh,

    The use of ILIM is fine if you are shorting D+/D- or not using the D+/D- functionality.

    To enter shipping mode, I recommend looking at Section 8.3.1.2.2 Shipping Mode of the datasheet.

    For USB unplugged and no on VSYS, you still need to follow the steps in Section 8.3.1.2.2 Shipping Mode to enter shipping mode.

    Correct, the charger does not include reverse polarity protection, but it does have overcurrent and overvoltage protection, but this is typically secondary to some thing like a standalone primary protector.


    Regards,
    Joel H