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Original question:

TCA9548A: TCA9548A with variable I2C interface level & RESET using I2C

TCA9548A: TCA9548A with variable I2C interface level & RESET using I2C

J.P.
Intellectual 300 points
Part Number: TCA9548A

1) I  would like to confirm if each channel SD0-7/SC0-7 can operate at different modes (ie SD0/SC0 @ FAST kHz Normal 100kHz) or is the speed related to the speed of the master? Therefore, if SDA/SCL is 400kHz, then all channels SD0-7/SC0-7 would be at 400kHz?

2) Also, I saw a previous post regarding Vpass. It appears that it I have any bus at 1.8V, then my VCC needs to be <=3V. However, SDA/SCL can operate at V_high=0.7*VCC-6.0V.

This means that I can have

a) A channel at 1.8V

b) VCC=2.5V

c) SDA/SCL=3.3V

Did I miss anything here?

Thank you!

  • 0
    TI__Guru 63000 points

    Hey JP,

    1) The speed is related to the master and what the slave is capable of supporting. Our device supports 400kHz frequency so the master can communicate at this speed without worries of signal integrity being corrupted by our device. If you are operating at 400kHz but the slave is not capable of this, then the slave should not be connected to I2C bus during the 400kHz communication.

    To reiterate, all channels do support 400kHz but if the slave cannot handle 400kHz then it is best you isolate it (keep the channel disabled).

    2) Our inputs (SDA/SCL pins) have 5V tolerance so if Vcc is at 2.5V and SDA/SCL is at 3.3V the device will not be damaged.

    "Also, I saw a previous post regarding Vpass. It appears that it I have any bus at 1.8V, then my VCC needs to be <=3V."

    That is correct, if the main channel's pull up voltage meets Vcc*70% AND meets the requirements in figure 14 (pass fet stuff you mentioned) then the device should work properly.

    From the details you have provided, I don't see a problem here.

    "Did I miss anything here?"
    -I don't think so.

    Only other "gotchas" I can think of:
    If you are connecting switches in parallel or series or use really strong pull up resistors (low value resistors) then you may want to be careful how many channels you turn on at once due to how pass FET architecture set up works .

    Thanks,
    -Bobby

  • 0 in reply to BOBBY
    Intellectual 300 points
    thanks!