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BQ24600EVM: Battery not charging

user4300350
Intellectual 310 points
Part Number: BQ24600EVM
Other Parts Discussed in Thread: BQ24600

Hi there, 

I have recently ordered the bq24600EVM (HPA421) to evaluate. I performed the test listed on the User Guide successfully. I was able to do: 

  • AC ADAPTER DETECTION THRESHOLD Test
  • CHARGER REGULATION VOLTAGE Test
  • CHARGE CURRENT Test

When I switched my DC load with a LiPo battery I wasn't able to see any charge current. This test was done without a load on VSYS 

  • STAT: blinking
  • CHGEN: on
  • PG: on 

VBAT was configured to 14.7V charge voltage by replacing R15 with 110Kohm resistor. 

Questions:

  • What can cause the charger not to recognize the presence of the battery ?
  • The EVM BOM shows a 10mohm Rsense that defined the maximum charge current but the board is configured to allow only 3Amax. What's the actual value of Rsense (i will measure that later but if you could confirm that it'd be great)

Below is a picture of my setup. 

 

  • 0
    TI__Guru 56650 points
    What is the input voltage, VREF pin voltage and TS pin voltage?
    On the EVM, the sense resistor should be 10mohm
  • 0 in reply to Wang5577
    Intellectual 310 points

    Vin = 20V
    Vref = 3.3V
    TS pin voltage is set with a power supply to 1.8V and then 2V

    WIth 10mohm the maximum current should be 10A according to equation 2 on the datasheet.

    There are some discrepancies on the datasheet and the EVM. The datasheet says the charging current is 3A, according to my calculation that means Rsr would be .033ohm

    The datasheet BOM specifies Rsr QTY 2, the schematic shows only 1. 

    Even with 2 Rsr in series, the Charge current would be 5A

  • 0 in reply to user4300350
    TI__Intellectual 2050 points

    Hi,

    How did you determine that R15 should be 110kohm to achieve 14.7V charge voltage?

    Using the equation below, 110kohm would achieve 19.4V charge voltage. I calculated 151.1kohm to achieve 14.7V charge voltage. Please switch R15 with a 151kohm resistor and see if it charges. Let me know if you have any other questions.

    Thank you,

    Joe

  • 0 in reply to Joe Stephan
    Intellectual 310 points

    Joe, 

    Thanks for checking my calculations. I noticed it as well right yesterday when i was comparing the VLOWV with the VFB i was measuring. I changed the voltage divider to 130K and I got my battery to charge at 3A.  

    I changed the inductor to 1.5uH and added a 20uF cap on the output but I still can't charge at full charge current. Any idea what's happening? 

    Thanks

  • 0 in reply to user4300350
    TI__Intellectual 2050 points
    Are you saying you changed R15 to 130kOhm?

    Measure the voltage on ISET. What voltage do you see? Should be 2V to achieve 10A charge for a 10mOhm sense resistor.

    Also, what is the battery voltage? It is possible that the battery is at the regulation voltage and the charger is now tapering the current as it approaches termination.

    -Joe
  • 0 in reply to Joe Stephan
    TI__Intellectual 2050 points
    This was resolved by user4300350, "Joe, i was able to figure out after sending my last post that i needed to configure the resistor divider on ISET to allow for 10A charge current."

    -Joe
  • 0 in reply to Joe Stephan
    Intellectual 310 points
    I have a follow up questions about using 2 separate bq24600 in parallel to increase my charge current to ~19A. I'd actually like to design a fast charger that will charge a 20A LiPo. So i was thinking about using the 2 charger in CC mode and disable 1 of them when starting the CV mode.
    Do you have some thoughts about the feasibility of such an architecture .
    What potential issues can come out of such an implementation.

    Thanks
  • 0 in reply to user4300350
    TI__Intellectual 2050 points
    Can you please post this follow up question to the new thread I created for you?
    Link: e2e.ti.com/.../2282281 user:231029#2282281

    Thank you,

    Joe