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BQ25703AEVM-732: How can I tell it is charging?

Thu Nguyen
Prodigy 130 points
Part Number: BQ25703AEVM-732
Other Parts Discussed in Thread: BQ25703A

Hi, 

I want to charge 1 cell 18650 Lithium battery by BQ25703A EVM. I tested the board as well as downloaded the software following the user's guide and datasheet of the chip. I powered the board up by 5V and I did not connect the load to VSYS. I took JP2,3,4 off and connected a 3.7V 18650 battery and measured roughly 16 mA flowing and 3.6V across it. I left it connected for 2 hours and the current decreased to 0mA. That makes me think that the battery was discharging all the time not charging. In the software, under charge status register, it said not either in fast charge or in pre-charge. 

Can you help me how to recognize if it is charging or what I can do (changing which register?) to have the battery charging? I think the board is set to charge the battery as default, is that correct?

Thank you!

  • 0
    TI__Mastermind 24075 points

    Hi Thu,

        Charger is not set to charge by default. The charge current register default value is 0A. Host has to write a value to this register. In this part, charger is disabled by writing 0A.

  • 0 in reply to Kedar Manishankar
    Prodigy 130 points

    Hi,

    I just set the charge current limit to 256 mA and the current meter read 256.6mA. I checked the battery with my charger before I connected to the board, my charger showed the battery was 63%. After I connected the battery to the board, although the meter showed there was some current flowing, after half an hour, I took the battery out and checked with my charger, it displayed only 37%. That makes me think it was discharging. Can you help me with this? What else should I do to have the battery charged?

  • 0 in reply to Thu Nguyen
    TI__Mastermind 24075 points

    Hi Thu,

       If charge current set is same as actual charge current observed, then I would expect the register is being configured correctly. Do you have a system load connected that could be draining the battery? Take a scope capture of the charge profile over 30 minutes, capturing VBAT, VBUS, VSYS and IBAT.