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TCA9617B: About Max speed

[FAE] Andrew Wang
Genius 10685 points
Part Number: TCA9617B

Hi Team,

Customer is using TCA9617B as I2C repeater.

And customer would like to verify with us for 2 things, please help!

(1)

In our app note:

The summary said: The 1000-kHz operation of FM+ I2C bus when using repeaters is limited to certain loading conditions on the I2C bus.

Customer would like to know what is "certain loading conditions" actually meant? Customer wants to reduce the loading as much as possible.

(2) Customer would like to double check with us.

In our app note, we pointed out the actual top speed due to repeater propagation delay，at 1MHz, it can be only 872.8KHz。

customer would like to know if this can be improved by any  optimization on PCB/schematics or other trick?

Thanks.

Andrew

  • 0
    TI__Mastermind 49270 points
    Hey Andrew,

    (1) "certain loading conditions" refer to the bus capacitance/pull up resistors. This can increase due to how many devices you add to the I2C bus and what value of resistors you pick for pull ups. We typically estimate 10pF per device.

    (2) "if this can be improved by any optimization on PCB/schematics or other trick?"

    -This comes back to the first question. In the parameters listed, we can say that the propagation delays on the devices are fixed. This means the other parameters "could" be played with to get us better results. These parameters however are usually dependent on the bus capacitance..... You can decrease rise times by using stronger pull up resistors where max resistance is dependent on capacitance. Fall time will be dependent on the bus capacitance of the I2C bus so you would need to lower your bus capacitance to get faster fall times. <-- usually this parameter is small already and will have marginal max frequency bonuses. Set up data parameters depend if rising or falling and go back to load capacitance and pull up resistor values.

    It should also be noted, this 872.8kHz frequency is derived used worst case allowable parameters based on I2C max allowable specs and datasheet worst case scenario specs. In terms of PCB, try to keep traces short to reduce capacitance.

    Thanks,
    -Bobby