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Original question:

BQ51050B: bq51050B Wireless Power Receiver and Wired Charger - Replacement for bq24040

BQ51050B: how to use a BQ24072 into an Application for Wired Charging

gustavo zarba
Expert 1080 points
Part Number: BQ51050B
Other Parts Discussed in Thread: BQ24072, , BQ24040

Hi, 

continuing with the question, wether I can use a BQ24072 on the the example of Pag 32 of the bq51050B datasheet (Figure 37.  Wireless Power Receiver and Wired Charger)

The BQ24040 on the application has only one pin (OUT) to charge the battery and supply the system.

However, the BQ24072 has one OUT pin to connect the System and one BAT pin to connect to the battery and charge it.

There is a FET (Q2) connecting both pins internally. 

My question is:  is it possible to tie BAT and OUT externally together?

Thank you in advance for your help,

Gustavo

  • 0
    TI__Mastermind 22150 points

    Hi Gustavo,

    There's no problem using the BQ24072 in place of the BQ24040 as shown in the example. It is not intended for the BAT and OUT pins to be connected together as the OUT pin is  a BAT tracking output. When using the BQ24072, connecting the BAT pin to the +Pack is fine. You can leave the OUT pin on the BQ24072 floating with a capacitor connected if it is not used.

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Expert 1080 points

    Hi Anthony,
    thanks for the quick reply.
    It surprises me a bit. I understand that de OUT is the output for the system supply. The datasheet says:

    OUT: System Supply Output. ... Connect OUT to the system load.

    The possibility of connecting the load directly to BAT is clear, but then I would lose the capability of feeding the system with the USB-Voltage, when the battery has low charge, for instance.
    Is there a way to keep both possibilities?

    Best regards,

    Gustavo

  • 0 in reply to gustavo zarba
    TI__Mastermind 22150 points

    Hi Gustavo,

    With a BQ24072, you'd be able to connect your load to the OUT pin. You'll still be able to charge wirelessly through the BQ51050B and power the load at the OUT pin of the BQ24072 while the BQ24072 OUT pin is supplied by the battery if no USB power is present.

    When USB is present, as mentioned in the BQ51050B datasheet in 9.2.2.1 Design Requirements for wired and wireless charging, the FETs will activate and the BQ51050B disables the BAT pin. The USB power can then go to the IN of the BQ24072 with the FETs and charge the battery while powering the OUT load.

    gustavo zarba said:
    The possibility of connecting the load directly to BAT is clear, but then I would lose the capability of feeding the system with the USB-Voltage, when the battery has low charge, for instance.

    This is not true with the BQ24072 as you connect the system to the OUT pin despite the bat tracking feature. You'll see in Figure 8-4. BQ24072 Output Regulation Voltage vs Battery Voltage that the OUT voltage will remain at 3.4V until VBAT is greater than 3.2V. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Expert 1080 points

    Hi Anthony,

    I think, now I get it: I was assuming that I need to have my load on the OUT pin from the BQ24072 for wired charging and on the battery by wireless charging.
    It was not clear to me that the BQ24072 would still be funktional during wireless charging.

    So, the conclusion is: The load should only be on the OUT pin of the BQ24072, regardless of the charging method and not on the battery. Is this correct?

    Thanks again and best regards,
    Gustavo

  • 0 in reply to gustavo zarba
    TI__Mastermind 22150 points

    Hi Gustavo,

    Yes, as described in the previous reply, the B51010B will go high impedance on the BAT pin when an adapter is present, letting the BQ24072 charge. When wireless charging method is used, the BQ51050B will charge the battery as no power will go to the BQ24072 at the IN pin.

    gustavo zarba said:
    So, the conclusion is: The load should only be on the OUT pin of the BQ24072, regardless of the charging method and not on the battery. Is this correct?

    Yes, this is a feature of power path devices such as the BQ24072. You can find more in the 9.3.4 Dynamic Power Path Management section of the BQ24072 datasheet that explains this feature.

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Expert 1080 points

    Thanks Anthony, this was very helpful.
    I now see the way.
    Nice from you, to work on a Saturday!
    I wish you a nice Weekend,

    Best regards,

    Gustavo