On the Vref on ADC(MCP3208)

[shemo]

VIH of MCP3208 is 0.7VDD which is 3.5V. Why on this circuit the Vref is 4.096V? Also why there's a zero jumper connecting 5V and 4.096V?

 

[barry]

wow.

Vih has nothing to do with Vref.

The reason Vref is 4.096 is because the designer wants full-scale to be 4.096. It could be 2.5 or 1.25 or 3.3959395.


Without showing us the rest of the schematic there's no way to know what the function of that zero ohm is, but my GUESS is that it gives you the option of using the 5V supply as Vref if you leave the regulator out.

 

[shemo]

so if the regulator is there and with 4.096 V and ties to 5V , what would be voltage of these two superimposed together?

 

[barry]

Don't do it.

 

[shemo]

wow.

Vih has nothing to do with Vref.

The reason Vref is 4.096 is because the designer wants full-scale to be 4.096. It could be 2.5 or 1.25 or 3.3959395.

WHy is VREF relates to the full-scale. Isn't vref relates to the triggering pointing? Above that is registered as hi and below as low.

for example I used the 3.3V DRAM before and its VREF would be 1.65V, the middle of 3.3V.

 

[crutschow]

You are confusing the digital thresholds with the analog input resolution. Vref determines the full-scale (all 1's output) value for the A/D input. You do know what an A/D does, don't you?

 

[barry]

WHy is VREF relates to the full-scale. Isn't vref relates to the triggering pointing? Above that is registered as hi and below as low.

for example I used the 3.3V DRAM before and its VREF would be 1.65V, the middle of 3.3V.

Wow, again.

Do you have any idea what this device does? It most certainly is not a DRAM, why did you even mention that?

Maybe you should read the data sheet.....