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Original question:

BQ25756: Can we use BQ25756 vith BQ7694?

BQ25756: Can it be used through hardware only not via I2C?

Hiroshi Ransom
Prodigy 30 points
Part Number: BQ25756
Other Parts Discussed in Thread: BQ76942

Hi TI team,

The BQ25756 charge controller we intend to use with a battery pack: LiFePo4 8S1P 29.2V battery.

Can you describe any way to use this charge controller by just triggering input pins?
I have read the manual and it appears that charge cycles can only start when amongst other things, the EN_CHG bit on REG0x17 is set to 1 via I2C.

For our setup we had intended to use the BQ25756 with a BQ76942. In this related post I've extrapolated that these two ICs will be compatible.
https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1281031/bq25756-can-we-use-bq25756-vith-bq7694?tisearch=e2e-sitesearch&keymatch=BQ25756#



If there is a way to operate the BQ25756 without I2C, can you confirm that the BQ76942 will work well in combination with the BQ25756 IC?

If there is no way to operate the BQ25756  without I2C can you suggest any other LiFePo4 charge controllers which don't require I2C to operate, which are compatible with the BQ76942?


Thank you,

Regards

Hiroshi Ransom

  • 0
    TI__Genius 17320 points

    Hello Hiroshi,

    Yes, the charger can be operated without I2C commands. You can use resistors to control charge voltage, charging current, termination current, INDPM, VINDPM, and more. Charge can be turned on and off by pulling down the CE pin high and low.

    The BQ25756 should work well with the BQ76942.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 30 points

    Hi Ethan,

    Thanks very much for your fast response the datasheet for the BQ25756 says:

    A new charge cycle starts when the following conditions are valid:
    "Battery charging is enabled (EN_CHG = 1 and CE pin is LOW )" maybe that needs to be an "or" if they are revising the doc.

    I had a similar question regarding the  BQ76942. From what I have read, configuration of this IC must be done through I2C to monitor a LiFePo4 8S1P 29.2V battery.

    Is there a way without I2C to configure the cell count, fault outputs DCHG, DDSG and all other required settings?


    Thank you,

    Regards
    Hiroshi Ransom

  • +1 in reply to Hiroshi Ransom
    TI__Genius 17320 points

    Hello Hiroshi,

    EN_CHG is set to 1 on power up so pulling the CE pin LOW or HIGH will adjust the charge even without I2C.

    Let me loop in the experts on the BQ76942.

    Best Regards,
    Ethan Galloway

  • +1 in reply to Hiroshi Ransom
    TI__Mastermind 35260 points

    Hello Hiroshi,

    The BQ76942 is able to work standalone, without I2C. However to program the settings, like the cell count and fault outputs, the part needs to have these OTP'd (One time programmable) into the memory, this would have to be done through I2C. This can be done with an external set-up, once OTP has been done, I2C is not required. 

    Here is an FAQ that talks about the OTP for this device family:

    Additionally, for more detail you can read Section 3 OTP Programming of the  BQ769x2 Calibration and OTP Programming Guide.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Ethan Galloway
    Prodigy 30 points

    Thank you Ethan and Luis,

    You've both covered off on my questions for the hardware that's great we have the charge controller operable without I2C,  have a great festive season.


    Regards,

    Hiroshi Ransom