SBOA323A December   2018  – June 2021 OPA333 , TLV9002

 

  1.   Design Goals
  2.   Design Description
  3.   Design Notes
  4.   Design Steps
  5.   Design Simulations
    1.     DC Transfer Results
  6.   Design References
  7.   Design Featured Op Amp
  8.   Design Alternate Op Amp
  9.   Revision History

Design Steps

V o u t = V d d × R 1 R N T C + R 1 × R 2 | | R 3 + R 4 R 2 | | R 3 - R 4 R 3 × V d d
  1. Calculate the value of R1 to produce a linear output voltage. Use the minimum and maximum values of the NTC to obtain a range of values for R1.
    R N T C M a x = R N T C   @   25 C = 2 . 252   k Ω ,   R N T C M i n = R N T C   @   50 C = 819 . 7   Ω
    R 1 = R N T C   @   25 C × R N T C   @   50 C = 2 . 252   k Ω × 819 . 7   Ω = 1 . 359   k Ω 1 . 37   k Ω
  2. Calculate the input voltage range.
    V i n M i n = V d d × R 1 R N T C M a x + R 1 = 3 . 3   V × 1 . 37   k Ω 2 . 252   k Ω + 1 . 37   k Ω = 1 . 248   V
    V i n M a x = V d d × R 1 R N T C M i n + R 1 = 3 . 3   V × 1 . 37   k Ω 819 . 7   Ω + 1 . 37   k Ω = 2 . 065   V
  3. Calculate the gain required to produce the maximum output swing.
    G i d e a l = V o u t M a x - V o u t M i n V i n M a x - V i n M i n = 3 . 25   V - 0 . 05   V 2 . 065   V - 1 . 248   V = 3 . 917 V V
  4. Solve for the parallel combination of R2 and R3 using the ideal gain. Select R4= 1.5 kΩ (Standard Value).

    R 2 | | R 3 i d e a l = R 4 G i d e a l - 1 = 1 . 5   k Ω 3 . 917   V V - 1 = 514 . 226   Ω
  5. Calculate R2 and R3 based off of the transfer function and gain.

    R 3 = R 4 × V d d V i n M a x × G i d e a l - V o u t M a x = 1 . 5   k Ω × 3 . 3   V 2 . 065   V × 3 . 917   V V - 3 . 25   V = 1023 . 02   Ω
    R 2 = R 2 | | R 3 i d e a l × R 3 R 3 - R 2 | | R 3 i d e a l = 514 . 226   Ω   × 1023 . 02   Ω 1023 . 02   Ω - 514 . 226   Ω = 1033 . 941   Ω
  6. Calculate the actual gain with the standard values of R2 (1.02 kΩ) and R3 (1.02 kΩ).
    G a c t u a l = R 2 | | R 3 + R 4 R 2 | | R 3 = 510   Ω   + 1 . 5   k Ω 510   Ω =   3 . 941 V V