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Original question:

BQ25155: I2C control register compatible replacement part

BQ25155: Using I2C with BQ25155 without routing /LP line

Dushyantha Jayatilake
Prodigy 230 points
Part Number: BQ25155
Other Parts Discussed in Thread: BQ21061

Is there a way to use ADC values and I2C communication without routing /LP? What if I directly connect /LP with LSLDO?

Due to manufacturing cost constraints (to avoid laser buried via), I'd like to avoid using /LP, however my understanding is /LP is internally pulled down and at that state when Vin is unavailable, the device is in a low-power mode, with no ADC or I2C. I still want to use both these to regulery check battery level, use watchdog features and use /MR as an ON/OFF switch.

I2C and ADC are impossible without connecting /LP to high, right?

Is low-power mode unavailable if /LP is connected to high?

Best regards,

Dushyantha

  • 0
    TI__Genius 12485 points

    Hi Dushyantha,

    You can take a look at the design strategies highlighted on this app note. Let me know if you have any further questions. 

    Regards,

    Gautham Ramachandran  

  • 0 in reply to Gautham
    Prodigy 230 points

    Thank you so much, Gautham.

    Just would like to double check with you. I do need a battery level monitor, so I guess BQ21061 is out. Also, my board manufacturer doesn't like <0.3mm pads, so 4.5mil D3 to C4 routing is not possible, unless I also go through NC1 (C3). But seems like NC1 should not be connected to any power.

    I'm having a push-button on /MR and thinking of also connecting it to the microcontroller while leaving /LP of BQ2515 floating and use Design B idea to enable I2C only when about to read. What do you think?

    Best regards,

    Dushyantha

  • 0 in reply to Dushyantha Jayatilake
    TI__Genius 12485 points

    Hi Dushyantha,

    11mil(0.3mm) seems pretty wide. A lot of PCB manufacturers can work with around half that like 6mil spacing. Can you please confirm if copper clearance has to be 0.3mm? This will be routed in between pads underneath the soldermask.

    You can certainly go with Design B which is leaving /LP float (internally pulled down) and use /MR as a way of putting the part into active mode and perform I2C communication. You might want to add an NMOS similar to the design so that it doesn't overvoltage stress the GPIO of the MCU and also prevents any unintentional wake from the MCU when going to shipmode. (unless your MCU can truly have the GPIO in HiZ in shipmode) No concern from the charger side at all- just to watch for the MCU IO as the /MR pin is internally pulled up to VBAT through a 120kohm resistor. 

    Also note that the /MR can possibly hardware reset so if you are pulling the pin low through the MCU- it is best to turn OFF that feature or keep I2C transaction window < /MR reset timers. 

    Let me know if you have any questions. 

    Regards,

    Gautham Ramachandran

  • 0 in reply to Gautham
    Prodigy 230 points

    Hi Gautham,

    With 11mil (0.3mm) I was refering to the BGA pad size. I think the chip footprints are based on a pad size of 0.2-0.25mm, but our board manufacturer always requested us to change them to 0.3mm to lower manufacturing cost.

    Thanks for the warnings. I'll be careful with the input design. Also, I preaume my I2C transactions with BQ are going to be less than 1s in duration, unless when I really want to shutdown.

    Btw, just to reconfirm, just in case, can I route /LP to LSLDO make the device always run in standard mode?

    Best regards,

    Dushyantha.

  • 0 in reply to Dushyantha Jayatilake
    TI__Genius 12485 points

    Hi Dushyantha,

    Routing such way will have a higher current consumption at all times as the device is in active mode. So i dont usually recommend that. 

    Regards,

    Gautham