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BQ33100: BQ33100 capacitance measurement

Charles Bergren
Prodigy 130 points
Part Number: BQ33100
Other Parts Discussed in Thread: EV2400

Greetings.

I've been taking capacitance measurements from the BQ33100, and I always seem to get the same answer.  I must be doing something wrong.

The manual indicates the following fw procedure

8.5.2.2.8 Capacitance (0x10)
This read- or write-word function returns an unsigned integer value, with a range of 0 to 65535, of the predicted
full charge capacitance in the super capacitor pack. This value is expressed in F.
Table 51. Capacitance
SBS CMD 0x10
MODE R/W

NAME Capacitance

FORMAT Unsigned Integer

SIZE IN BYTES  2

MIN VALUE 0

MAX VALUE 65534

DEFAULT VALUE  —

UNIT F

I have, I believe, 6/5 farads in the design.  The answer I get back is always 13 (0x000D).  This is uniform across a population of boards.  I have the feeling I must be doing something wrong.

  • 0
    Prodigy 130 points

    Doc3.docx      A screen shot of the I2C transaction is in the docx file

  • 0 in reply to Charles Bergren
    TI__Mastermind 25955 points
    Hi Charles,

    What is the value stored in InitialCapacitance? Is this value the same as the value in Capacitance?

    Has the bq33100 performed the learning process prior to reading the Capacitance?

    Is the device running in NORMAL mode or STACK mode?

    Please fully charge your supercapacitors and ensure that V Learn max and V CHG Max are set to the maximum charging voltage as specified by the capacitor manufacturer.

    Upon device reset, the bq33100 estimates the initial capacitance, however, super capacitor capacitance learning is required in order to improve the accuracy of Capacitance and RSOC.

    Next, please perform a qualified capacitance learning. When the device is in unsealed mode, the Learning Frequency is set to every 10 minutes. To avoid waiting, try issuing the ManufacturerAccess Learn command.

    The device will set CL = 1 and clear LPASS in Operation Status when the qualified capacitance learning cycle begins. When a qualified learn has occured, LPASS will be asserted.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 130 points

    Thanks for the prompt answer. So a few things

    Operation Cfg - looks like it is contained within the flash.  We do not have the source for the flash contents nor the tool necessary to view the flash contents.  We only have a binary file which we load into the BQ33100 flash.  I'm not sure I can easily answer your question about Operation Cfg without either disassembling the flash or obtaining the tool.  Is the tool easy to get and can it disassemble the binary file we have?.  I could send you the binary file by private email so it can be identified.

    InitialCapacitance - is also in flash.

    Operation Cfg - While I have not observed the value of this yet, the following statement from the manual IS correct according to the schematic I have.

    When in Stack mode (Operation Cfg [STACK] =1) VC1 must be connected to VC2 and VC3 connected to VC4.
    Additionally a divide-by-2 resistor divider must connect between the top and bottom of the capacitor array with
    VC1,2 being the top and VC3,4 being the middle and VSS being the bottom. In this configuration pins VC5 and
    VC5BAL are not used and must be connected to VSS.

    I believe learning takes place once per minute; the ESR value we fetch back from the BQ33100 changes at that pace.

  • 0 in reply to Charles Bergren
    TI__Mastermind 25955 points

    Hi Charles,

    I apologize for the delay in response.

    To be able to check the parameters of the monitor, please connect the EV2400 to your custom board.

    EVSW + EV2400 will be able to talk on your communication lines with the bq33100 and allow you to see this data in real time and also export a .SENC file of the gauge settings.

    Please let me know if there are any issues or difficulties barring you from these steps. If so, we'll find another way.

    Sincerely,
    Bryan Kahler