Author Topic: Sensor to ADC - OpAmp design  (Read 911 times)

0 Members and 1 Guest are viewing this topic.

Offline raff5184Topic starter

  • Regular Contributor
  • *
  • Posts: 213
  • Country: us
Sensor to ADC - OpAmp design
« on: May 09, 2019, 04:32:54 pm »
Hi,
I'm following this tutorial http://www.ti.com/lit/an/slyt173/slyt173.pdf
 
to design an OpAmp to be placed between a sensor and an ADC.
On page 4, section "Determining resistor values", it says "Let RG = 27 kΩ". Why? How is it chosen?\

Thank you
 

Offline No.Mad

  • Regular Contributor
  • *
  • Posts: 73
  • Country: pl
Re: Sensor to ADC - OpAmp design
« Reply #1 on: May 11, 2019, 01:04:40 pm »
Hey raff5184,

from my understanding the value 27k is basically put as an example of calculating the rest of resistances and the whole process of adjusting values to those accessible on market.

If you compare it to E24 Series, resistor values like 21k, 51k, 270R and so on are widely available from any online shop or Ebay.

So simply speaking: it was used as an example for calculations. You could put any value for Rg and calculate the rest as shown.

Regards
 
The following users thanked this post: raff5184

Offline MasterT

  • Frequent Contributor
  • **
  • !
  • Posts: 851
  • Country: ca
Re: Sensor to ADC - OpAmp design
« Reply #2 on: May 11, 2019, 03:59:22 pm »
 R1 & R2 is a load for Vref. Compromise is to keep R1 R2 as low as possible, since
Quote
" RG >> (R1 + R2) then (R1 + R2) and R1||R2
can be neglected"
, and not to overload Vref. Basically, calculation is should be done in reverse, first select R1 R2, than take RG about 100x of R1||R2 (1% tollerance) and last step is calculate RF.
 
The following users thanked this post: raff5184


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf