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BQ24295: Slow Charging: Wireless Power Input (no D+/D-)

Andrew Baek
Intellectual 915 points
Part Number: BQ24295
Other Parts Discussed in Thread: BQ25619

Our circuit uses BQ24295 with a wireless power receiver.

The wireless power receiver outputs ~5VDC.

The battery capacity is 320 mAh so theoretically the charging current should be limited to 160 mAh.

As there is no USB input, D+ and D- pins are left floating.  Perhaps this is an issue afterthought.

We tried to set the limit and the charging current 

  • reg_write_byte(0x00, 0x5a);
    • 1A (100)
    • If we choose 500 mA (010), it doesn’t seem to charge
    • ILIM is 1K
  • reg_write_byte(0x02, 0x1C);
    • Charge Current 448 mA
    • The battery capacity is 320mA

Also we added a Schottky diode to prevent the current from flowing in the reverse direction.

The issue is that despite the sufficient charging current set up in the register and ILIM, the battery doesn't seem to get charged.

The wireless power should provide enough current at 5V, > 500 mA.  

Is there some D+/D- detection we would need to disable since they are left floating?

Or how should we terminate them since there is no USB input.

The attached Powerpoint shows the circuits for BQ24295 and the wireless power receiver (STWLC68 from STMicro).

Regards,

Andrew

notes 032324.pdf

notes 032324.pptx

  • 0
    TI__Mastermind 24735 points

    Hi Andrew, 

    Thank you for reaching out via E2E. Please see my comments below.

    For your application there should be no issue with leaving D+/D- pins floating. The BQ24295 will detect floating D+/D- pins as an unknown adapter and set input current limit in REG00 to 500mA. 

    Regarding your register settings REG00 set to 0x5A is good to set IINLIM  = 500mA. REG02 set to 0x1C will set ICHG = 960mA (This is shown on page 34 of datasheet). Based off your description it seems you want to set ICHG to minimum setting of 512mA. To set minimum ICHG write a value of 0x00 to REG02. 

    To further debug why you cannot observe charging please help to answer the following questions. 

    -Have you confirmed the wireless receiver is actually providing a stable 5VDC to VBUS pin when attempting to charge? 

    -Does BQ24295 device regulate SYS output at a voltage above your battery voltage?

    -When attempting to charge can you read from status and fault registers (REG08 and REG09) to see if they indicate any issue?  

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Intellectual 915 points

    Hi Garret,

    Here is a set of the registers I am using now

    REG00: 5A
    REG01: 3B
    REG02: 0
    REG03: 0
    REG04: A0
    REG05: 9C
    REG06: 3
    REG07: 4B
    REG08: 2C
    REG09: 0
    REG0A: C0

    For REG03, I am using the minimum value because the battery size is only 320mA. 

    The minimum value is 128mA but is there a way to lower it even further?

    For REG04, I lowered the full charge voltage.  I use BQ27421 for fuel gauge, and was able to observe 100% battery level.

    Also lowered the pre-charge voltage.

    REG07: I lowered the PMID voltage to save the power.  In the next board spin, I can also use this to drive 3.3V LDOs.  

    Previously I was concerned that I would lose too much power if PMID was at 5.0V but with the lowered voltage it may make sense.

    Again I was able to charge to 100% and am now testing how long it would take to discharge to < 10%.

    I would then charge again to see how long it takes to reach 100%.

    The only thing I am still concerned about is REG03 for pre-charge/termination current.

    With the battery size being only 320 mA, I am concerned that the charging would stop prematurely with 128mA termination current.

    Regards,

    Andrew

  • 0 in reply to Andrew Baek
    TI__Mastermind 24735 points

    Hi Andrew, 

    Glad to hear you can now charge your battery. Please see my comments on your remaining concern below. 

    Andrew Baek said:
    The minimum value is 128mA but is there a way to lower it even further?

    There is no way to further lower the precharge and termination current settings. 128mA is the minimum. If you determine this setting is critical we have other charger IC options, such as the BQ25619, which are designed to operate at lower currents. The BQ25619 has a minimum allowable precharge and termination current of 20mA. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Intellectual 915 points

    Hi Garrett,

    I think BQ25619 would be a perfect fit for our needs.  

    Our product is a wearable location tracker with wireless power receiver.

    We will update our design accordingly. 

    Regards,

    Andrew