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BQ40Z50-R2: CTO timer reset condition

yann
Prodigy 180 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50,

Hello,

I am doing cycles and I got a unexpected end of charge. Looking at safetyStatus, it looks like it has been caused by CTO protection. Here are the parameters related to CTO in my config:

CTO Charge Threshold: 150mA
CTO Suspend Threshold: 100mA
CTO Delay: 25000s
CTO Reset: 2mAh

From the lack of documentation and from this post:  I assumed the CTO timer would reset when discharging for at least CTO reset.

Here is a plot showing when the charge stopped:

And for reference a similar plot when the charge didn't stopped:

So my question is basically that: What exactly are the conditions for CTO timer to reset? Is this a buggy feature that I should avoid?

BQ40Z50-R2 is updated to v2.11.

  • 0
    TI__Guru* 81034 points
    Hi Yann,

    You have the correct understanding of the CTO reset parameter. I cannot see anything from your settings or your waveforms that would explain why you would see the CTO protection trigger.

    However, I do see that the device temperature is rising very fast during charging. Are you sure that you are not seeing an OTC fault? The default setting for the OTC protection is 55C. I do not see it go to this temperature on your data graphs, but do you see any samples that reach this temperature (the default delay is only 2 seconds for this fault)?

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Prodigy 180 points

    Hi Matt,

    Thanks for the input. For your concern about temperatures, it is only the BQ40Z50 internal temperature that goes up, cell temperatures (physically measured on the battery pack with exported ntc) don't go above 30°C and in "configuration - Temperature Enable" I removed TSInt (value is 0x1e).

    Here similar plots showing the safety status and alert flags. We can see that this is actually the CTO flag that gets triggered and not the OTC.

  • 0 in reply to yann
    TI__Expert 6575 points
    Hi Yann,
    What is your DSG current Threshold?
    You have to discharge for 2mAh and be in discharge mode (|Current()|> Dsg Current Threshold) to reset the CTO timer.
    I am suspecting that the current is not going below the DSG threshold and so the CTO timer is not being reset.
    If this is not the issue, please attach your log file with this issue, it will be easier to figure out the issue using the log.
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 180 points
    Hi Swami,

    Nice catch! Indeed "Dsg Current Threshold" is set to 100mA and the discharge current is is just under it.

    So for completeness, the response to my first question: What exactly are the conditions for CTO timer to reset? is:
    A discharge of at least "CTO reset" of the capacity most occur while in discharge mode which occur when "Current < -Dsg Current Threshold".

    Thanks !