I made a design using BQ24610 to charge a 4-cell battery pack to 16.8V. It seemd working well in prototypes and was released to production. When the sales person demostrated the product frequently, some devices showed strange behaviors occationally:
The battery charger charged the battery for a while, then stop charging. No LED turned on, and never recovered even all enable charge conditions were valid. The only way to activate the charging again was unplugging-plugging the AC adaptor. The chance to see this behavior happenning is ~20%. Since the charge cycle was pretty long, it took a while to catch the problem.
But it couldn't be explained after I read the datasheet carefully. In the beginning I though it could be thermal shutdown with high die temp, but if that was the case the charger should soft-start again once the temperature dropped. I didn't think it was TTC timer fault because I had more than 5 hours for timeout. I saw it happened twice in an hour after AC adaptor plugged. I used 18V adaptor to charge 14.8V (16.8V full charged) battery pack, there was no chance for input over-voltage or under-voltage.
It seemed the charging action was suspended, but I could figure out the cause. By the way, the battery temperature was not monitored, the TS voltage was set to constant 1.7V with voltage divider. My fast charge current was set to 2A, the precharge/termination current was set to 0.3A.
Does anybody notice the similar problem? Could it be a bug for the IC itself?
Thank you for answering my question.
With LED turn off, it must one of these conditions:
Timer fault: based on your description the timer should not be the issue.
Over voltage: do you experience any over voltage conditions on either the battery or the input.
Sleep mode: do you have a condition when the input voltage falls bellow the battery voltage? or Vcc< SRN.
Battery absent: if the battery is, it should recover as the battery comes back. But in your case, it never recovers.
Send me the schematic for review.
In reply to Tahar Allag:
Sorry I was not aware of your reply. I just got your followup notice today.
Actually the situation got worse: we had sales person complained the problem and sent two units back yesterday. The charge always stopped .
All the conditions listed in your reply seem not eligible for our case:
Timer fault: the 56nF cap connecting to TTC gives 313 minutes for fastcharge timeout. The charge suspension happened always between 30min to 90min.
Over voltage: we use 18V adaptor to charge 4-cell battery to 16.8V. Even there is spike from the adaptor, it stop the charging temperarily. The charge should restart in a moment.
Sleep mode: it should not happen. Even the Vcc drops lower than SRN for a couple microsecond (I don't think it happens), the charge should restore once the Vcc voltage gets over SRN.
Battery absent: it is impossible. We have a reliable connector for the engagement.
The schematic is attached. Please let me know if you don't get it.
In reply to Daniel Chen59387:
Just some addtional information: the two units returned from the sales sites repeated the charge suspension at my office. Both units were charged from exaust condition this morning. Charging suspension happened TWICE for BOTH units so far. The valid charge peroid was around 60 minute (more than 30min precharge timer) each time.
When the first suspension happened, I measured the battery voltage was about 14.4V; when the second suspension happened, I measured the battery voltage was about 15.1V. I also measured the VCC voltage which was about 17.6V, 2~3V above SRN.
I appreciate if you can help to find the cause quickly.
I reviewed the schematic and it looks good.
I am trying to understand what causing the shut down. As far as I know, we do not have this complain before.
Can you please send me some scope plots just at the time the IC shuts down? Look at the pins that behave unusually during that time (overshoots, drops...etc). This will help us understand the cause of the shut down.
Since the cause of the suspension is unknown, I don't have clear idea where and what signal to monitor. No scope plot captured so far.
Not sure if you get the second message I sent yesterday:
Some addtional information: the two units returned from the sales sites repeated the charge suspension at my office. Both units were charged from exaust condition this morning. Charging suspension happened TWICE for BOTH units so far. The valid charge peroid was around 60 minute (more than 30min precharge timer) each time.
When the first suspension happened, I measured the battery voltage was about 14.4V; when the second suspension happened, I measured the battery voltage was about 15.1V. I also measured the VCC voltage which was about 17.6V, 2~3V above SRN
I also measured the voltage on TTC pin yesterday. I noticed: when they charger was suspended, the voltage on TTC pin was 1.238V, which was in the middle of TTC osc low threshold (1V) and TTC osc high threshold. When I unplugged the 18V input, the voltage dropped to 0V; re-plugged the 18V input, the voltage jumped to 1.238V mometarily then dropped to about 1.05V and stayed there.
From the tests in last couple days, I feel the suspension problem are from one of below causes:
1) TTC timer is not accurate or disturbed by the switching noise, so gives faulty time-out signal;
2) The state machine inside the chip is triggered to "fault" state by power spike or switch noise, which can't be recovered by itself.
In my next test, I will connect TTC pin to Vref to disable the safety timer. It will tell if the TTC timer is the cause.
I appreciate if you can send me some details regarding the TTC timer/counter inside BQ24610 chip. I want to know if I can connect TTC pin to a voltage other than GROUND and Vref.
You can’t use other voltage other than GND and Vref. That is because the TTC has internal current source to charge up the cap then discharges it as it reaches a high threshold level. A counter is used to count the number of cycles. The time of each cycle is adjusted by a cap on the TTC pin.
Let me know what happens when you pull up to Vref if the issue goes away. Also you can probe it and see if there is a clean signal on it.
Do you know what happen in the TTC pin yet? Is the operation of the TTC pin helped zoom in into the issue?
It was verified to be true that the safety timer ran at much quicker pace than expected, possibly triggered by the switching noise in the system. Tying the TTC pin to Vref solved the problem.
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