Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

  • State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 32 subscribers
  • Views 1789 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TCA9548A: Cascading and multi-voltage

Wai Kei Pong
Prodigy 10 points
Other Parts Discussed in Thread: TCA9548A

Hi,

I have two questions regarding TCA9548A I2C switch. Please refer to the block diagram below for both questions.

1. Cascading two TCA9548A switches

Is it OK to cascade two TCA9548A switches? That is, SC0/SD0 port of the first TCA9548A is connected to SCL/SDA port of the second TCA9548A. The master will always be on the SCL/SDA port of the first TCA9548A, and it needs to be able to go through both switches to reach the slaves at the very end of the tree. If so, is there any special design considerations or limitations that I should be aware of?

2. Level translating for 1.8 V slaves

I will have the master and most of the slaves in 3.3 V, but a few slaves will be in 1.8 V and will be connected to only one of the TCA9548A ports, say SC7/SD7. What VCC voltage should I use for that TCA9548A? If VCC needs to be at a low voltage, how does it affect the VIL/VIH and VOL of the TCA9548A so that it works for both 3.3 V and 1.8 V ports?

(Modified picture from TI TCA9548A datasheet)

Thanks,

Wai Kei

  • 0
    TI__Expert 5140 points

    Hi Wai,

    Thank you for the question. 

    This operation is a common question asked to us on the forums. This configuration of switches is fine to use, but there are some application limitations to be aware of. 

    1. Make sure that you do not exceed the IOL specification that is listed in the datasheet. With more devices, you can expect this value to be higher.

    2. Be aware of your bus capacitance. With more slave devices you can expect a higher value of load capacitance on the I2C line. We usually use a typical rule of thumb of about 10pF per slave device.

    3. Ensure that you have control over the address if they will be doing independent actions.

    As for the VCC that needs to be set to ensure optimal operation. Please make VCC equal to the lowest voltage on the Channels. in this case, this will be 1.8V. The reason for this is to ensure that we are meeting the pass gate specification:

    Thanks,

    Siby