TCA9543A: Cascade I2C Multiplexer

Pablo Liberman1

Part Number: TCA9543A
Other Parts Discussed in Thread: TCA9546A, SN74LVC2G66, SN74HCS74, SN74LVC1G79, SN74LVC1G175

Hi,

I would like to know if this is possible:

I think it is wrong because there is an address conflict, all TCA9543A have the same address.
Could you confirm this?

Thank you!

5 months ago

+1 Clemens Ladisch 5 months ago

Guru 277260 points

Yes, this circuit has address conflicts. (And cascading too many switches can increase the V_OL level too much, but the TCA9543A has only four possible addresses.)

0 Pablo Liberman1 5 months ago in reply to Clemens Ladisch

Prodigy 70 points

Thank you,

V_OL problem could be solved by buffering, unfortunately I can't find a simple solution for the address conflict.

0 Clemens Ladisch 5 months ago in reply to Pablo Liberman1

Guru 277260 points

What is the maximum number of modules? Would it be possible set address in hardware (e.g., jumpers)?

0 Pablo Liberman1 5 months ago in reply to Clemens Ladisch

Prodigy 70 points

In my case the maximum number of modules is 10. With the TCA9546A I can reach 8 devices. Not bad.
Because the product will be manufactured in large scale, it would be difficult to set a different address for each device.
Of course, an MCU could solve the problem, but it would add the task of programming the firmware.
I evaluted the LTC4316 address translator, but it is too expensive.

0 Clemens Ladisch 5 months ago in reply to Pablo Liberman1

Guru 277260 points

How many signal lines can be used? The only practical way to address modules by their position would be to implement a shift register. Build the shift register with flip-flops (e.g., SN74LVC1G79), and use their outputs to control a plain switch (e.g., SN74LVC2G66) to connect the I²C devices to the common bus. (The power-up state of flip-flops is undefined, so you should initialize them by clocking in ten zero bits, or use flip-flops with a /CLR input like the SN74LVC1G175/SN74HCS74 with a reset signal.)

0 Pablo Liberman1 5 months ago in reply to Clemens Ladisch

Prodigy 70 points

Hello Clemens,

First off all, thank you for helping me.

That's a great idea. I must tell you that I had already thought about it.
The only drawback is that you have to add 2 wires to the bus. It's a cost-benefit choice.

The other option with 2 cables + VDD + GND

0 Clemens Ladisch 5 months ago in reply to Pablo Liberman1

Guru 277260 points

The other option would require a MCU and two switches (for the slave devices and for the downstream bus). I do not know what the hardware and software costs are; this is your choice.

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TCA9543A: Cascade I2C Multiplexer