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PCA9546A: PCA9546A schematic review request

Part Number: PCA9546A
Other Parts Discussed in Thread: TCA9543A

Hi TIer, 

Will you help to take a look on the schematic and let us know if you have any comments/concerns? 

Thank you, 

  • We are sending the design out for fabrication on Monday and I would really appreciate if you could provide your comments back today. Thank you. 

  • This schematic does not show the required pull-up resistors on I2DATA/I2CLK. I assume they are placed on another part of the schematic.

    PUP1/2/3/4 have very small values. (Please note that the buses are not isolated; the pull-up resistors on any enabled downstream channels are in parallel with those on the upstream channel.) I would make them 10 kΩ, unless you need to drive a bus with a very large capacitance.

    You can connect /RESET directly to VCC, unless you want to force the pin low during debugging.

    A two-channel switch like the TCA9543A would be smaller.

  • Hi Jason,

    Pullup resistors should be present on both sides of the device. SDA/SCL to SDx/SCx is not isolated by a true buffer, only a simple switch is between these two channels. This makes it so that when a channel is activated, you will see the combined pullup resistance to VCC in parallel. If you have 1kohm resistor on SDA, and 1kohm resistor on SD0, effective resistance will be a little over half ~500ohm. These are strong pullups, and could result in the I2C bus unable to pull the bus low. Only include strong pullups if the bus contains high amounts of bus capacitance, otherwise it would be good to increase resistance to something like 10kohm (like Clemens suggested). 

    /RESET should be connected to VDPUM (VDPUM is the master/controller I2C reference voltage) through pull-up resistor if not used.