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BQ34110: Shutdown mode and storing remaining capacity in data flash

Part Number: BQ34110

Hello,

I need to use Shutdown power saving mode, but I need that when the device turns on again the Remaining Capacity has a valid value.

Q1) I understand this is possible because of the available information in BQ34110 Technical Reference Manual, items 3.2.56, 3.2.57 and Table 3-2. Am I right?

Q2) However, I tried the following:

a) Shut down and turn on the chip
b) During microcontroller operation once every 1 second I send subcommands STORE_REMCAP_A and STORE_REMCAP_B (1ms separation between these two subcommands) to store RC in data flash
c) Same as (b), but sending a Device Reset command after turning on

In all of these cases the RC after turning off and on is different from the actual remaining capacity.

I tried these options based on the available information in BQ34110 Technical Reference Manual, but it seems that this information is unclear or incomplete. Please give some further instructions on how to achieve the RC storing and retrieval from data flash.

Thanks in advance,
Gustavo

  • Hola Gustavo ,
    Thank you for your interest in bq34110. A BMS expert has been assigned to your question.

    Regards,
    David
  • Hi Gustavo,

    A1 and A2) Please see Section 2.7.10 of the TRM for information on how REMCAP is determined when the device is initially reset. Section 3.7 of the TRM describes that RemainingCapacity() is a read-only command that returns the compensated battery capacity remaining.

    As described in section 2.7.10, this value is based upon both RemCap Init Percent value correlated to the battery voltage table. RemCap will track FCC, not the absolute capacity entered in the device.

    Please increase the time between writing the commands to ~30 ms or greater and repeat your test both before and after a learning cycle to see if the values now track FCC as expected.

    Sincerely,
    Bryan Kahler
  • Bryan,

    I did increase the time between writing commands STORE_REMCAP_A and STORE_REMCAP_B to 50ms, but the problem persists: When the device is reset, the Remaining Capacity is not initialized with the value the gauge had before writing these commands and shutting down, such as the TRM specifies in 3.2.56 and 3.2.57.

    I'm not sure if you understood my questions, because I'm not worried about FCC, but about the present state of charge of the battery (eg: 30% SOC remaining).
    I expect that after shutting down and up again, the state of charge preserves the value it had before shutting down.

    Unfortunately, although the text seems to be clear (3.2.56, 3.2.57 and Table 3-2), the TRM once again fails to specify a predictable behavior for the BQ34110. As I mentioned in other posts, following this trial and error procedure to guess what the TRM meant to specify isn't a good deal. Specially when testing requires long charge + discharge cycles, and the documentation is 109 pages long.
    Keep in mind that the customer relies solely on this documentation, hence the importance that it's as clear and reliable as possible.

    Gustavo
  • Hi Gustavo,

    In the preferred usage of a gauge, the gauge would not be powered off. The gauge operates by coulomb counting both charge and discharge.

    Before the device is powered off, the SOC may indicate one level based upon coulomb counting and several other parameters including loading and temperature. Upon power up of the device, error may increase until the device has completed a charge cycle. This error may be exacerbated if the battery is powered off/on in the 'flat region' of the battery voltage to DOD curve.

    There are methods to reduce the error if the gauge must be operated in this manner, but are application specific. Please provide more information with respect to the application so we may discuss steps to take.

    For example, is removing power from the gauge a hard requirement? If so, why?

    Sincerely,
    Bryan Kahler
  • Bryan,

    Removing power from the gauge is not a hard requirement. My intention is to minimize power consumption during off cycle.

    Since other off currents (including self discharge of the pack) are around 100uA, I expected to lower gauge consumption from the specified 28uA (22uA during SLEEP mode + 133uA during NORMAL mode, with 20 seconds period).

    If this energy gain requires many complex procedures (development time) in order to not lose stored SOC, then I prefer to keep the gauge in power up permanently. I believed that it was a simple task, that's why I started this post.

    Thanks,

    Gustavo