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BQ24401: BQ24401 Trickle Charge Question

Part Number: BQ24401

I'm using the BQ24401 to charge 3s NiMH batteries 3.6V 1600mAH.

I'm using a 5V input to the charging circuit this voltage drops to 4.5 though the diode.

Circuit is set up for a max current of 500mA. 

Everything seems to be working ok. I'm curious about the trickle charge. I plugged a battery pack in that's been drained to 0.9V.

The trickle charge begins and seems to be working but it seems to bring the battery back to a certain point then it can't get past it.

The voltage at the BAT pin is between 608-650mV and the battery voltage is up to 1.8-2.0V. You can see the current on the 5v line pulsing at 50mA.

It has been on for 18 hours.

Is there something in the circuit I can adjust to get the trickle charge to push past this point and kick into fast charge?

Thought about increasing the Rmto to even out the duty cycle a little I currently have a 39.2K and Cmto is 0,15uF.

Please advise.

  • Jerry,

    The bq24401 will stay in the battery conditioning state indefinitely and will not progress to fast charge until the voltage on the BAT pin is above VLBAT. It could be possible that the pack is damaged. Can you try a battery pack with voltage higher than 3V? How much is the Vcc and what is the state of LED?