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PCA9306: PCA9306DCUR

xujunfeng
Intellectual 290 points

Part Number: PCA9306
Other Parts Discussed in Thread: TCA4307

Tool/software:

i2c 400Khz，use PCA9306DCUR to trans 3.3v to 1.5V.

but the 3.3v input rise time is not meet 1.5v slave requst

please help me。

  • 0
    TI__Guru 50281 points

    Hi Xujunfeng,

    I2C specifies the max rise time of a 400KHz to be 300ns max, which looks to be a violation in the waveform. The concern is that the slow rise time could cause communication errors as the downstream device may not be able to detect the rising edge of the 3V3 driver.

    Note the observed slow rise time is directly impacted by the pullup selection used, as well as how cap. loaded the I2C bus is. Could we try using stronger pullups and also share a schematic for further checks as needed? 

    Regards,

    Jack 

  • 0 in reply to Jack Guan
    Intellectual 290 points

    Our investigation found that buffer affected it and it was ADI LTC4307. Is there any model that is Pin-to-PIN compatible recommended?

  • 0 in reply to xujunfeng
    TI__Guru 50281 points

    Hey Xujunfeng,

    The TCA4307 would be the P2P option to the LTC4307. You may also refer to Sections 8.2.1- Section 9 of the datasheet for good design practices with this device. 

    Regards,

    Jack

  • 0 in reply to Jack Guan
    Intellectual 290 points

    The TCA4307 also seems to have a precharge function, which doesn't seem to solve our rising edge problem

  • 0 in reply to xujunfeng
    TI__Guru 50281 points

    Hey Xujunfeng, 

    I see- thanks for clarifying. If hot-swap is not a requirement, you may also see the TCA980x without the precharge function (this buffer uses an integrated current source on B-side, so no pullups needed on B-side).

    Regards,

    Jack