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bq24072 charge current problem

Steve Lyon
Prodigy 50 points
Other Parts Discussed in Thread: BQ24072

Hi,

I am using the bq24072 linear battery charger IC and seem to be experiencing an issue relating to charge current.

I wanted to charge at 450ma so I set Riset=2k, and an overall current limit of 1A so set Rilim=1.5k, but I am only seeing 180ma going into the battery as measured with a DMM. This is over several hours of trying to charge an 1800mah battery starting at 3.5V so I don't think it was a spurious reading.

Other details of my system are: 5V charge source capable of sourcing 1A, TMR floating (to select default safety timers), EN2=high, EN1=low, TD=low, the rest of the system (@ the OUT pins) is drawing at most 45ma.

Does anybody have any ideas about why I am not able to achieve 450ma charge current?

Thanks,

Steve L

  • 0
    Prodigy 10 points

    You give some absolute values for resistors but not the values of the other resistor in the dividers.  The charge current and adapater current limits are established by a voltage on pins 5 and 6.  This voltage is compared to the voltage measured across the sense resistors after applying gain.  Be sure to use the equations on page 19 of the data sheet.

  • 0
    TI__Guru**** 150830 points

    Your component values look reasonable.  We need to debug this piece by piece.  Disconnect everything from OUT and see if the issue still occurs.  Use a known good input supply that can provide over 1A.  Look at IN with a scope and make sure the voltage there is stable and the 5V that you think it is.  What voltage are IN, OUT, and BAT at?  Is this on the EVM or your own board?  Was the IC mounted properly?