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TMUX1208: I can't change the channel in TMUX1208

Mariusz Profecki
Prodigy 40 points
Part Number: TMUX1208
Other Parts Discussed in Thread: TMUX1108

Hello.

I'm trying to use TMUX1208 as a demultiplexer with one input passes to the D pin, and 4 outputs (S1-S4). When all A signals are off I can see that S1 is on and the other channels are off - it's ok. The problem is when I'm trying to change the channel. For example if I put A0 to 1 A1 and A2 to 0 (which should turn the S2 on) I can still see the signal on the S1 pin and not on the S2. The same happens when I'm trying to use S3 or S4, there is always signal only on S1 :( What can be wrong? Do I have to buy a new part, because the one I have has some defect?

  • 0
    TI__Genius 9132 points

    Hi Mariusz,

    Can you confirm that the EN pin is pulled high?

    Can you share your setup of TMUX1208 and signal scope shots for  more details?

    Thanks

    Saminah

  • 0 in reply to Saminah C
    Prodigy 40 points

    Hi. Yes I put 3V to the En pin, the same to the Vdd. To the GND I give -1.5V as a reference signal, so to the A0...A2 I put -1.5V as well when I want to have them low (S1 enable). To enable S2 for example I'm pulling A0 to 0V and A1 and A2 to -1.5V so it should be situation just as in the datasheet. Right now I;ve replaced the old Tmux for a new one but the problem still occurs. I'm giving a sine wave to the D pin. it's -700mV to -70mV more or less.

  • 0 in reply to Mariusz Profecki
    TI__Genius 9132 points

    Hi Mariusz,

    If you look at the pin functions table for TMUX1208, it specifies to have GND to 0V reference.

    Also mentioned in the recommended operating conditions of this part,  Vs or VD range from 0V to VDD.

    Can you try setting GND to 0V and pull the A pin to 3V when you are switching between channels? 

    Also, please look at TMUX1108 that has same configuration as TMUX1208 but offers wide dual supply Range: ±2.5 V, 1.08 V to 5.5 V.

    Using this switch, you can set VDD to 3V, VSS to a negative -1.5V, and maintain the supply rail difference of 4.5V which is in the recommended operation conditions of TMUX1108 as shown below.

    Thanks

    Saminah