TL431 A2D Voltage Reference Question

[hal9001]

I want to use the TL431 as a 2.5 volt reference connected to a A2D input. VCC is 3.3V. How do I size the R2 resistor from this example circuit? Is it (VCC-2.5)/Required current? Where required current can probably be 1mA as its going into a A2D input?
Thanks

[Terry Bites]

R1= (Vcc-2.5)/(Iload+Imin)
Imin from datasheet- say 1mA.

[not1xor1]

I want to use the TL431 as a 2.5 volt reference connected to a A2D input. VCC is 3.3V. How do I size the R2 resistor from this example circuit? Is it (VCC-2.5)/Required current? Where required current can probably be 1mA as its going into a A2D input?
Thanks

what do you mean ? The input current of the ADC is 1mA ?
TL431 minimum current is usually 1mA. So you can use a resistor of (3.3 - 2.5) / (1+1) ≈ 390 Ω or less.
In any case there are better (more stable and accurate) yet still cheap voltage references than TL431.

[hal9001]

R1= (Vcc-2.5)/(Iload+Imin)
Imin from datasheet- say 1mA.

Thanks I understand now!

I want to use the TL431 as a 2.5 volt reference connected to a A2D input. VCC is 3.3V. How do I size the R2 resistor from this example circuit? Is it (VCC-2.5)/Required current? Where required current can probably be 1mA as its going into a A2D input?
Thanks

what do you mean ? The input current of the ADC is 1mA ?
TL431 minimum current is usually 1mA. So you can use a resistor of (3.3 - 2.5) / (1+1) ≈ 390 Ω or less.
In any case there are better (more stable and accurate) yet still cheap voltage references than TL431.

I think I understand the resistor sizing now thanks. Kindly, what are some examples of better voltage references for cheap?

[not1xor1]

I think I understand the resistor sizing now thanks. Kindly, what are some examples of better voltage references for cheap?

LT1009 has better accuracy, less thermal drift and surely better long term stability than a generic TL431. It is more expensive... probably around 50 cents. There are better references but those would cost a few USDs.