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Original question:

BQ40Z50EVM-561: Difficulty getting the Battery Management Studio to recognize the device correctly

BQ40Z50EVM-561: Device not recognized when the EVM is powered with a load connected

Marco Villa
Intellectual 290 points
Part Number: BQ40Z50EVM-561
Other Parts Discussed in Thread: EV2400, BQSTUDIO

Hello

I succeded to use the bq40z50EVM with the EV2400 and bqtudio. I'm simulating a battery pack 3Swith an external power (3.7 x 3 = 11.1V) an 3 x 1K resistors as suggested in the manual.

In these conditions, after powering the EVM and pressing the Wake button the device is properly recognized. In the same conditions but with a 10 Ohm load connected between PACK+ and PACK-

the device is not recognized!!! But if I start with no load and after BQstudio has recognize the device I attach the laod everithing works fine. (for example issueing a DSG_FET_TOGGLE command I see about

1A flowing through the load).

I don't undertand why the device is not recognized in presence of a load when I power up the EVM. A possible reason is that the device in in SHUTDOWN but why?

Any help?

Thank

  • 0
    TI__Mastermind 42535 points

    Hi Marco,

    With a 10Ohm load you are pulling current and dropping Vbat below 2.2V, that leads to the gauge shutting down because it needs at least 2.2V to power up. This is mentioned in the DS page 5 and table 7.6. You can use a 1k resistor between PACK+ and PACK- to simulate a load. That will prevent shutdown.

  • 0 in reply to Batt
    Intellectual 290 points

    Hi Batt

    As I wrote, the EVM is powered by a power supply not by a battery pack: I checked with an oscilloscope and VBat rises regularly at 11.1V even with a load connected.

    Summarizing

    case 1: (OK)

    - EV2400 connected to a PC

    - No load connected between PACK+ and PACK-

    - Power on the EVM with a voltage of 11,1V simulating 3 x 3.7V Li-ion battery

    - pressing wake button after a few seconds

    - launching BQstudio, it recognizes the device and works

    case 2: ( KO)

    - EV2400 connected to a PC

    - 10 Ohm load connected between PACK+ and PACK-

    - Power on the EVM with a voltage of 11,1V simulating 3 x 3.7V Li-ion battery

    - pressing wake button after a few seconds

    - launching BQstudio, it DOESN'T recognizes the device

    In case 1) if I attach the load AFTER the BQstudio has started I can communicate with the device regularly.

    I can't explain why.

  • 0 in reply to Marco Villa
    TI__Mastermind 42535 points

    Hi Marco,

    Please don't use a 10 Ohm load, it won't limit the voltage drop at the PACK and that will cause the BAT voltage to follow it. I suggest using a 500 Ohm at a minimum or at least a load if you have one where you can limit the voltage.

  • 0 in reply to Batt
    Intellectual 290 points

    Hi Batt

    thanks for the quick reply but I still don't understand.

    Let me explain better. I think of using 3 Li-Ion batteries of 3.7V/2600mAh to power a string of power LED that tipically source about 1A.

    I expect to power the LED with a Driver that will provide a constant current but at the moment I don't have it yet.

    So I' m using 10 Ohm to be close as much as possible to the real case.

    Anyway I also connected a 1k resistor between PACK+ and PACK- and the result is the same: the device is not detected.

    Where could be problem? Can I lower the resistor R1 in series to Q1 the precharge FET (see the schematic of EVM) ?

    Regards

    Marco

  • 0 in reply to Marco Villa
    TI__Mastermind 42535 points

    Hi Marco,

    If your FETs are on, your battery voltage is going to follow your pack load voltage plus some delta. If this BAT voltage is lower than shutdown, you will shut the gauge down. That's what's happening in your case. I have not seen an issue with a 1k between PACK+ and PACK- on the evm.