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BQ35100: I2C bus

Part Number: BQ35100
Other Parts Discussed in Thread: TPS61070, , TIDA-01236

Hello,

Regarding the board TIDA-01236, there's the arrangement as described in the related document TIDUCU1 as using a TPS61070 as a boost converter used for two purposes, feeding 4V for the buzzer and powering and enabling at the same time the BQ35100, this has several issues as described below:

1. BAT has voltage from the battery even when REGIN, the main input voltage for the device, does not.

2. GE is supposed to be low for the chip to be powered off, the only "pull-down" I see is that from the feedback pin for the boost regulator, more than 2M. Obviously the chip wouldn't have direct power, but I wonder if some internal circuitry would run if it "draws" power from the I2C pull-up resistors.

3. There are obviously pull-up resistors on the I2C lines, which would put voltage on the BQ31500 inputs even when powered off, the input protection on most ICs are diodes to the power rails, so it would "parasitically" power it and put extra leakage drain on the battery and well, put voltage on the un-powered chip.

Is the implementation on that reference board validated and characterized to behave as intended in ultra-low power applications?

I don't know, am I missing something here?

Thanks.

  • Adrian,
    1. This does not cause any problem with the chip. The IC will not be powered on in that case and the pin leakage would be just be the standard leakage as defined in the device data sheet.
    2. No. There is no such internal circuitry.
    3. The i2c pins of the chip are open drain.

    yes, the implementation on the reference board was validated.
    thanks
    Onyx
  • Thanks for the response Onyx,

    I understand your responses, I'm still not quite sure on number 3, I mean, the I2C circuitry is still CMOS, and is not supposed to be voltage applied to a CMOS input without the circuitry having power. I get that it is open-drain, but still there will be voltage applied to the input via the pull-up resistor and the thing is that I cannot find anything on the datasheet, not even a diagram of the I/O ports.

    I see that you are a TI employee, is there more thorough information available on this chip?

    Thanks in advance.