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TCA9543A: TCA9543A channel switching time

Part Number: TCA9543A

Hi Team,

What is the time delay between sending the commend to switch the channels and to have the channels been switched actually? Is DS describing this?

Piotr

  • Hey Piotr,

    The datasheet does not explicitly state this data, I suspect this is not a common problem and the delay time is short enough due to a guaranteed by design kind of situation. I realize this kind of answer doesn't actually give you an answer but I can give you atleast a range of what should be the max values here.....

    This device will not actually enable switches until it receives a stop condition by the master:

    This device was also made to follow I2C timing requirements and so if we consider the amount of time is allowed between a stop and a start condition we can atleast narrow down this range to an acceptable level.

    The buffer time here states a minimum of 4.7us and 1.3us are required between a stop and start condition on the I2C bus for 100kHz and 400kHz respectively. Therefore the switch times need to be below this value in order to meet I2C standard and for the channels to be ready to communicate once the start condition begins......

    One other thing to consider is how the channels are actually enabled:

    You can see above, each channel is controlled by a FET. One parameter FETs have is called a gate charge which is the minimum amount of charge the gate must see before turning on. This gate charge parameter is usually shown in a FET datasheet as well as a parameter called delayed turn on time, which is dependent on the gate charge and parasitics of the gate (capacitance and resistance). I've typically seen this time be shown in nanoseconds so I would expect our device's FETs to also have a low nanosecond turn on time. The input filter and I2C bus control will likely have it's own delays but by the time this device ACKs and the master releases the bus I suspect these delays are over. It's likely the delay is the delayed turn on time of the FETs.

    -Bobby