• State
  • +1 person also asked this people also asked this
  • Replies 3 replies
  • Subscribers 16 subscribers
  • Views 96 views
  • Users 0 members are here
Support feedback
Options
Options
Related

TMUXS7614D: Questions about the Daisy Chain Mode

TI-CSC
Genius 13750 points
Part Number: TMUXS7614D


Hello E2E Experts,

Good day.

We are currently using two of the TMUXS7614D ICs on one of our circuit boards. These ICs are wired for use in Daisy Chain Mode. The ICs are wired as follows:
- V_DD = 5 V 
- V_SS = GND
- V_L = 3.3 V
- TMUX 1 S1-S5 are connected
- TMUX 1 S6-S8 and TMUX 2 S1-S2 are connected
- TMUX 2 S3-S7 are connected
- TMUX 2 S8 is floating
- TMUX 1 D1 is connected to a 1 V test voltage
- TMUX 1 D6 is connected to a 2 V test voltage
The other Dx Pins are currently floating.

Now, a quick initial question:  Did I understand the datasheet correctly in saying that, for this setup, a voltage range of -0.5 V to 5.5 V is available for V_Sx and V_Dx?
We are planning to use the TMUX with a higher voltage later, so we need to consider which supply voltages to use. 

Now, on to the real questions/problems. I am currently implementing SPI communication for this setup, with the goal of being able to select one of the five sub-channels for the three main channels (the Sx pins connected together). I want to use daisy-chain mode. 

I am currently sending the 0x2500 command to the first TMUX. Using the SDO pin from the second TMUX, I am reading back the 0x2500 command with the µC in the same cycle. Is this behaviour correct?

I am now assuming that the two TMUX are in daisy mode. I then tried sending two 16-bit commands, 0x01FF, to enable all the switches. In my opinion, this should be the correct way to set up the switches. However, in my case, I measured the voltages of the main channels, and it looks like the 1 V and 2 V are not being switched through the TMUX. Have I missed anything?

I then tried sending the command 0x01FF three times to check the SDO pin of the second TMUX with an oscilloscope, but no communication was seen.

I also tried controlling only the first TMUX by writing the command 0x01FF once, but this did not work either. When I tried this, I disabled the initialisation of daisy mode. 

I assume that the SPI communication should work, since I can enable daisy mode, but it seems that I cannot enable the switches on the two TMUX. 

My next step would be to scratch the circuit board to check the signals, as we do not have test pins for all of them. This might help us to identify the error. However, I may have made a mistake with the SPI communication. That's why I wanted to ask for help in this forum.

Regards,

TICSC

  • 0
    TI__Mastermind 19735 points

    Hello TICSC,

    The TMUXS7614D is a rail to rail part. You can only pass voltage levels up to its supply. In your application VDD = 5V, so you can pass signals from 0V to 5V on the Sx and Dx pins. This is the recommended operation. What you are referencing are stress conditions. 

    Yes, this behavior is correct.

    Please provide a schematic and pictures of the signals you are trying to send including CS, SCLK, SDO and SDI.

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    Prodigy 10 points

    Hello Nir, 

    Thank you for your reply and for clarifying on the recommended supply voltages. 

    For now, I can only provide the schematic. I will send the pictures of the signals soon. 

     
    For testing, I connected 1 V to CH1-1 and 2 V to CH2-1. 

    Please let me know if you have any questions about the schematic.

    Best Regards, 
    Nils

  • 0 in reply to Nils Wais
    TI__Mastermind 19735 points

    Hello Nils,

    Thank you for sharing the schematic. I don't see any issues in it. 

    I will wait for you to provide the signals.

    Thanks,

    Nir