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Original question:

BQ76952: How can I convert SPI communication mode to I2C communication mode?

BQ76952: Unable to communicate with SPI

Remco Kuipers
Prodigy 20 points
Part Number: BQ76952
Other Parts Discussed in Thread: , EV2400

Hi,

Iam working with the BQ7695201 and have an issue that I am not able to communicate with the device through SPI. (Since i got the SPI variant of the device)

Searching through the forum i couldn't find an answer yet.

I hooked up the TI EV2400 Interface board to my board and trying to communicate with it using Battery management studio, no success. (I am able to communicate with the EV2400 using the BQ76952EVM)

Here is my schematic:

Things that i have checked:

  • SPI voltage levels 3V3
  • Chargepump - Not working (but i understand that it needs to be turned on from software)
  • SPI frequency is 125khz
  • Added an external 3V3 voltage supply on REG1 since it is not outputting power itself.
  • EV2400 has its pinout on J6 180degrees switched compared to what is illustrateed on the top of the case apparently. So i connected that correctly

Any suggestions on what the problem might be?

  • 0
    TI__Mastermind 42060 points

    Hello Remco,

    What is the REG18 voltage? What about CP1? The charge pump should be active when the device is awake. What is not active usually is the pre-regulator REG0.

    Initially you want to wake the device by either pulling TS2 low or by applying a charger voltage on the PACK pin. You could also cause a brief short from the battery voltage to the PACK terminals, which should be enough to wake the device.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 20 points

    Hello Luis,

    Thank you for your reply.

    The REG18 voltage is 1.8V
    The CP1 voltage is the same as BAT voltage, in my case 30V that tells me the charge pump is not active.

    I tried waking the device up but no luck.

    I also found that i should have connected BREG to REGIN instead of GND. So that is now corrected.

    Also, there is some strange 1Vpp ripple (251Hz) on my BAT voltage only after the diode. I can see this ripple back on the MISO signal which is not responding with data.

    Regards,

    Remco

  • 0 in reply to Remco Kuipers
    TI__Mastermind 42060 points

    Hello Remco,

    It sounds like the charge-pump is getting discharged. This may be the ripple that you're experiencing as the charge-pump is trying to recharge. If this is not the case, then the IC may be damaged. If you could try with a different IC, we could confirm if it is damaged.

    Ideally the CP1 voltage should be ~11-V greater than the BAT voltage, so the voltage across the capacitor would be ~11-V.

    Did you see the same issue after BREG was shorted to REGIN?

    What kind of diodes are you using in your DSG/CHG circuit? I'd be worried there may be some current leakage there causing the CP1 capacitor to deplete.

    Any reason why you chose to use BQ7695201 instead of BQ7695204? BQ7695204 has REG1 enabled by default. With the current part, MISO would be ~1.8-V, the REG18 voltage.

    Best Regards,

    Luis Hernandez Salomon

  • +1 in reply to Luis H. S.
    Prodigy 20 points

    Hi Luis,

    I figured it out.

    Apparently some other device on the SPI bus caused Signal integrity issues and therefore the BQ7695201 did not respond.

    Also waking the chip only worked when adding the PACK voltage to the output of the system. (simulating a charger has been connected).

    Thank you for your respons.

    Kind regards,

    Remco