Team
I am posting the following question on behalf of a customer who recently experienced unexpected behavior while using a BQ24075T device:
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MicrosoftInternetExplorer4
I assembled my latest
design yesterday. Everything was working great. I fully charged up
1 cell and then discharged it pretty low (2.34V) The battery manufacturer
assures me that this is okay.
Last night I plugged the charger back in. I have the wall powered charge
current set to maximum and I measured it to be 1.5A. I observed the
battery voltage for a time and saw that it was charging. I went to sleep
and checked it in the morning to find the charge light still on. I
checked the battery voltage and it was a steady 3.35V. When I unplugged
the charger the battery voltage did not change indicating that it was not
charging (I was reading the battery voltage directly).
I could not understand what had happened. After playing around with it
for a while I thought the charge controller had died and I was contemplating
how I could unsolder it. Then I tried a test and disconnected the battery
and then reconnected the battery. I plugged the charger back in and the
voltage on the battery immediately came up to 3.38V and rising indicating that
the charger was now operational.
What happened?? I see nothing in the documentation that indicates a
charger lock-out condition. It is like somehow the charge controller got
stuck in a mode where it would not charge until the battery was disconnected
and then reconnected. 1.5A is the maximum charge current in the spec and
I was running at maximum. Is it possible that this was too much
current?? Still, once the charger was disabled shouldn't it self reset
once the ic cools down? I have a lot of copper on the board acting as a
heat sink. I have the bottom of the IC well soldered down to the
pcb. The chip gets hot to the touch. I would guess around 50
degrees C when charging at 1.5A and the surrounding board is probably
35-45. This tells me that the board is sinking heat away pretty good.
I am testing it now and the battery is nearly fully charged once again.
Working like a champ. Problem is I need to fully understand this lock-out
condition. If the product locks out when a customer has it then the
product becomes worthless. It will be packaged in a permanently sealed
container, never to be opened. Do you have any ideas??? Is there
someone at TI that might have a clue what happened??
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Please let me know if this is a problem you have observed before. If so, also let me know if there is a solution that will prevent this from happening.
Regards,
