Hi,

I am working on a design where I need to control two TI analog multiplexers — TMUX1108 (8:1) and TMUX1104 (4:1) — using a single enable signal from a microcontroller. When I am using 4:1MUX data the 8:1 MUX must be disabled. The setup is as follows:

• The MCU provides one GPIO as the Enable source.
• TMUX1108 receives this signal directly.
• TMUX1104 receives the inverted signal through SN74LVC1G04DBVR (single inverter).
• Both EN pins have 10 kΩ pull-down resistors to GND.
• All devices operate at 3.3 V.

Issue: At power-up, before the MCU initializes, the inverter input is at GND (due to the pull-down), so its output goes HIGH. This enables TMUX1104 immediately after power is applied, which is not desired. I want both multiplexers to remain disabled after power-up until the MCU explicitly enables them.


May I know,

What is the best way to ensure both TMUX devices are disabled at power-up

 

Use a 74LVC1G240, which has three-state outputs. Connect the processor to the OE pin. The outputs will be disabled until the processor starts running its program, and the pull-down resistors will keep the multiplexers disabled.
Alternatively, use a 74HC139 and connect one MUX enable to each output (there are four outputs, you will only need two) then its enable pin will switch both off.

 

Could try this mod.
Pulls enable low for appx 1 second or more when power is first applied.