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Tool/software:
Hi all,
I am posting this question again because unfortunately I can't find my previous post.
I designed my battery charging board based on TI BQ25750. Looks that almost everything works OK, except the STA1 STAT2 ports.
I charged an empty LiPo battery pack BB-2590/U up to its maximum voltage 33.6V (two sets of four batteries each, connected in series - 10Ah) . I followed the voltage during charging and it indeed behaved as described in the charger datasheet, but the two charger status bits didn't behave as expected - According to Table 8-6 I should get the following behavior:
But unfortunately only the first, third and forth states are working correctly . The second 'Charge done' state is not working - STAT1 remains ON and STAT2 remains OFF as 'Charge in Progress'. even after the battery voltage reached 33.6V during the Fast-Charge phase and the current reduced gradually down to only 10mA during the Taper-charge phase (the max charging current is set to 4A).
See below the relevant schematic parts:
Thank you for any assistance.
Shony
Hello Shony,
Can you provide your register information when this issue occurs?
Best Regards
Christian.
Hello Shony,
The registers values include the status registers and this will help me conclude how the device is behaving and help narrow down the issues.
Can you provide all of your register information when this issue occurs?
Best Regards,
Unfortunately i am just in the beginning of my board ramp-up. Can't read the registers yet. Hope that i will be able to do that soon.
B.R
Shony
Hi Christian,
I finally can read the charger status register REG0x21 and I found the following result:
When the battery voltage is ~33.4V and its current is ~80mA, the status register content is not stable - sometimes 04h (Tamper) and sometimes 07H (Termination).
When I check with scope the STAT1 and STAT2 pins I see them toggling between '01' and '10' in cyclic manner - ~2Hz. Seems they are indeed reflecting the register results.
Hope that it can give you some hint about the cause of this instability.
Best regards,
Hello Shony,
Thanks for working with this problem.
We recommend setting EN_PFM=0 when the battery termination current is less than 2A. Does setting EN_PFM=0 effect the behavior?
Best Regards,
Ethan Galloway
Hi Ethan,
I tried that. Unfortunately it wasn't helpful.
Anyway, I figure out that any register modification will not help, because I need it to work OK also while my system is power-off - the charger is powered but my CPU is off and can't control the charger.
Hello Shoney,
Thanks for letting me know. Let me get back to you later on this question.
Best Regards,
Ethan Galloway
Hello Shoney,
PFM can also be turned off by feeding in an external clock signal into FSW_SYNC. Is that an option for the system?
Best Regards,
Ethan Galloway
Hi Ethan,
I just figured out that the battery I am using is special one (BB-2590/U). It is combined of two independent battery packages, which I connected in series before charging with the BQ25750.
I think now that if the two are not fully charged and equalized carefully, the charger can't charge them correctly.
I tried two more batteries like it and found that each of them behave differently - one of them can't be charged at all and the second one charged 'correctly' and I finally got the stable Charging DONE from the charger.
And yet, even this third battery that fully charged is not absolutely OK, because I got the DONE only when the battery current reduced during tamper to only 30mA, instead of 400mA (10% of maximum defined charging current). I think that this is because even here the equalization is not absolutely fine.
So, this is very problematic battery. But I wonder if there is better, but yet simple, way to charge it?
B.R
Hello Shoney,
That is a strange battery.
Does the BB-2590/U have a battery monitor / battery gauge protector inside of it? Are there 2 devices or just 1?
Best Regards,
Ethan Galloway
Hi,
Yes. it has two complete battery packs inside. Each includes protection circuit, etc.
Meanwhile I discharged the 'good' battery and charging it again. Guess what? Now I got finally the DONE status as it should be - when tamper current reduced bellow 400mA. Case closed!
Hello Shony,
Glad to hear the battery is successfully charging. I'm going to mark this thread as resolved for now and I'll keep this in mind if I see this behavior again.
Best Regards,
Ethan Galloway