# Trying to multiplex voltage reference gives incorrect output

I'm trying to make the voltage reference for an INA214 opamp selectable between GND, 4.5V and 10V. I'm using a CD4051B multiplexer.

However, the 10V VREF gets pulled down to 5.84V, and I can't figure out why. simulate this circuit – Schematic created using CircuitLab

CD4051B has:

• INH, Vee, Vss to GND
• C to GND
• A, B to 5V (thus selecting CH3 as output)
• CH3 to GND
• CH1 to D1 output
• CH2 to D2 output
• Output measured by multimeter

Output measures:

• 4.95V when D2 is connected to any pin on the mux
• 0V when D2 is not connected
• 4.54V when B is GND, no matter if A is 5V or GND (D2 is not connected)

which is strange, because CH1 is A=1 B=0.

What is going here? Are the TL431s interfering with the function of the CD4051B, or...?

By the way, am I required to connect the other pins/channels to ground, or can they be floating?

• You don't say what you're powering the CD4051 with. I'm going to guess that it's 5V - in which case the problem is obvious - you can't pass voltages higher than your supply. – brhans Mar 27 '17 at 18:40
• @brhans, I read the following, from the datasheet, as though 4.5V Vcc would allow up to 20V channel input. Am I mistaken? "Control of analog signals up to 20V P-P can be achieved by digital signal amplitudes of 4.5V to 20V (if V DD -V SS = 3V, a V DD -V EE of up to 13V can be controlled; for V DD -V EE level differences above 13V, a V DD -V SS of at least 4.5V is required). For example, if V DD = +4.5V, V SS = 0V, and V EE = -13.5V, analog signals from -13.5V to +4.5V can be controlled by digital inputs of 0V to 5V." – user95482301 Mar 27 '17 at 18:47
• But maybe this is only for signals of negative voltage? – user95482301 Mar 27 '17 at 18:50
• I've generally learned to ignore anything in a datasheet which looks like it was written by someone in the marketing dept and focus on the tables, figures & diagrams ... – brhans Mar 27 '17 at 18:59
• Yes, you will need voltage translation. I suggest using simple NPN transistors as open collector, with pullup resistors. – bobflux Mar 27 '17 at 19:09 