Hi team,
My customer is evaluating our TL431Q1 product, they would like to know is that a must requirement for the following resistors R1, R2 accuracy be 0.1%, could it also be OK with accuracy 1% R1 and R2? Thank you!
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Hi team,
My customer is evaluating our TL431Q1 product, they would like to know is that a must requirement for the following resistors R1, R2 accuracy be 0.1%, could it also be OK with accuracy 1% R1 and R2? Thank you!
Hi Zirui
It depends on the error budget you are looking for. Let's say you are using 0.1% resistor and gain of 2 , in that case max mismatch will be 100.1k and 99.9K in R1 and R2. Hence max error in gain will be 0.1%. This error will increase to 1% in case you are using 1% resistance tolerance. Error due to resistance mismatch will increase with gain.
Hence maximum possible error % in VKA due resistor will increase 10 times when tolerance is changing from 0.1% to 1%. This error will get added in initial accuracy which is close to 2% [min  2.440 , typ  2.495 , max  2.550V].
Regards
Trailokya
Hi Rai,
Thanks for your reply. Now we would like to have an example calculation for our better understanding, please kindly help to check whether it is correct:
If both R1 and R2 customer use 0.1%, 10k resistors, please kindly confirm that whether they could obtain VO according to the following formula and table:
Note: Vref is 2.495 (typical), 2.470 (min), 2.520 (max) :

Typical 
% 
MIN 
MAX 
R1 
10.000k 
0.10% 
9.990k 
10.010k 
R2 
10.000k 
0.10% 
9.990k 
10.010k 
Vref 
2.495v 

2.470v 
2.520v 
Vo 
4.99 
0.10% 
4.985 
4.995 
In addition, there is another question, please help to confirm: Does the different value of Vsup input voltage also affect the result of VO output?
If I design directly according to Figure20, the Vka output is 2.47V~2.52V? Is that correct?
Thanks for your reply in advance!
Hi Zirui
Please refer below table
This gain error is calculated based on typical Vref for figure 27. VREF max to min will add extra error.
Figure 20 will not have much impact from R1 accuracy.
Regards
Trailokya
Hi Trailokya,
Thanks and customer is still wondering about the Fig 20 whether their understanding is correct: They would like to know the Vka value calculation based on Fig 20
"If I design directly according to Figure20, the Vka output is 2.47V~2.52V?"
Zirui
R2 in infinite in case for fig 20 so Vka = (1 + R1/(Infinite))*VREF so VKA will be equal to vref in that case irrespective of resistor tolerance value.
Regards
Trailokya