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bq24251 breaking current limits

Other Parts Discussed in Thread: BQ24251


I'm using a bq24251 to charge my battery and power my system.

I've already using it on another product, without problems, but on my new product, somehow it's not working accordingly.


R_ILIM = 0R (max 2A from input)

R_ISET = 165R (aprox. 1515mA)

0R between D+ and D-

0R between VDPM and GND

The problem arises when I set between 4.8V and 4.9V on the input. Somehow the battery current goes above 2A.

On this situation, VLDO jumps from 4.75V to 4.49V and VSYS from 3.90V to 4V.

I've measured the voltage on R_ISET. It's more or less 440mV when the current is as programmed, but it arises to 620mV when charging the battery with more than 2A.

The same thing happens (excessive charging current) when I configure the charging current on Register #4. I've managed to limit the charging current by configuring the ILIM on Register #2, but I want the device working on standalone.

On my another product, the voltage on R_ISET is always near 440mV and I had no problems with the charging current.

When the input voltage is > 5.1V the current behaves as programmed. There is some hysteresis because the voltages to enter and exit this condition are not the same.

Is there someone who can help finding where is the problem?

  • Hi Alexandre,

    It is possible that some layout/design change in your new board caused some instability. Can you try to add 10uF capacitor to IN or PMID. Also, try 10uF capacitor on BAT. To be effective, those caps need to be close to IC pins.

    You can also improve the situation by increasing VIN voltage. Or reduce IR drop on wires so that effective voltage reaching VIN pin is higher. This is specially helpful when at high current.

    Best Regards,