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Need 2>1 analog mux for higher-than-VCC signals

Need 2>1 analog mux for higher-than-VCC signals

Need 2>1 analog mux for higher-than-VCC signals

(OP)
Well dang it.  Didn't quite read the datasheet closely enough.

I have a car datalogger design that uses the DG333A quad 2>1 mux switch to multiplex the 16 input signals to 8 opamps for signal scaling for the ADC.  The part I didn't notice was the voltage limitation on the signal inputs ...

They can only range just above/below VCC and GND.  Since the datalogger is a 5V system, that kind of clobbers it for measuring vehicle 12V and above signals :(  The DG333A was chosen for the nice low 25ohm R-on value, and the fact that it had 4 switches in one package.

So, before I set about redesigning the analog input section, does anyone know of a quad (or any) 2>1 mux switch that can handle higher input voltages ?  Those inputs are fed via 180k resistors, so the total current is quite small.

If not, I have to rethink the analog input design strategy.  The requirement are :

16 inputs
jumper selectable input ranges (0-5V, 0-14V and 9-14V)
feed to 8 ADC inputs

I suppose I could put the opamps up front, and feed their outputs to the mux switches, but that doubles the opamp footprint, along with the attendant scaling resistors etc :(

Dean.

RE: Need 2>1 analog mux for higher-than-VCC signals

Put an R-R attenuator into each input line. Clamp
it to e.g. 4.5 V with Schottky-s or 4 V with regular
diodes.

<nbucska@pcperipherals.com>

RE: Need 2>1 analog mux for higher-than-VCC signals

You might look at Supertex for high-voltage muxes.

RE: Need 2>1 analog mux for higher-than-VCC signals

(OP)
Cool - thanks for the tips.  What exactly is meant by an R-R attenuator ?  How will that affect measuring a signal that ranges from 9-14V ?

Supertex has some high-voltage switches, but don't appear to hav ethe 2>1 muxes.  I'll keep looking.

Thanks -

Dean.

RE: Need 2>1 analog mux for higher-than-VCC signals

Vout = Vin*R1/(R1+R2) ; using 12 V ---> 4V then the attenuation is 1/3 i.e. R2 = 2*R1. Clamp it to less than 5V.
Select R1 and R2 according the load.

<nbucska@pcperipherals.com>

RE: Need 2>1 analog mux for higher-than-VCC signals

(OP)
Oh, got it.  You're just talking about a divider.  Doh.

D.

RE: Need 2>1 analog mux for higher-than-VCC signals

You are almost on the same track I am.
Try looking at the HCF4051B from STMicroelectronics.
It is an 8:1 MUX but you could easily cascade two of them together.

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