TMUX136: Unexpected output with EN_N is HIGH (TMUX 136 should be OFF)

Hi Clemens and Rami,

Both A1 and A2 output pin are floating. Only COM1 input pin is connected to clock generator and COM2 input pin is floating.

When EN_N is pulled HIGH (TMUX is OFF), A2 pin output is ~0V. But there is ~400mV at A1 pin.

If there is noise be picked up, then both A1 and A2 pin should have same behavior. 

Does it possible there is leakage from TMUX136 to A1 pin when EN_N is HIGH ?

Please feel free to comment. 

Thanks. 

Hey Woon Nee,

There is leakage but I wouldn't expect it to give you 400mV on the line. Is there anything else active on the board when testing? Is there any sort of board layout you can provide that may be of help? 
However, this still seems like noise. Could you provide a load and see what the results look like or is this only present when floating?

Thanks,
Rami

Hi Rami,

There is clock generator LTC1799 connect to SN74AXC4T245 (voltage translator) , connecting to input of TMUX136.

There is clock at the input of TMUX136 and we not expect to see DC output at A1/A2 when EN_N is HIGH (TMUX136 is OFF). 

What is the leakage that you expect ?

I will further to check with the load. 

Thanks. 

The OFF leakage current is specified as less than ±2 µA (±15 µA over temperature).

But anyway, a floating pin has a higher impedance than your oscilloscope input, so it does not make sense to measure it. If you want the disabled pin to be at 0 V, you have to add a pull-down resistor.

Hi Clemens,

The floating pin you mentioned here are refer to COM1/2 (input) or the A1/A2 pin (output) ?

The A1/A2 will be connected to 42.5ohm termination in system level. 

In your schematic, the A1/A2 pins are floatin when the TMUX is disabled.

Hey Woon Nee,

Off leakage is spec'ed in the datasheet but I don't believe that to be what you're seeing.

Have you tried measuring with a pulldown on the floating A1 and A2 outputs? This will give the potential somewhere to go. Otherwise, it's just floating.  

Thanks,
Rami