TLC2274M-MIL Datasheet, PDF (22/33 Pages) Texas Instruments – Advanced LinCMOS Rail-to-Rail Operational Amplifier

TLC2274M-MIL
SLOS985 – JUNE 2017
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However, as the resistors have tolerances, they cannot be perfectly matched.
R₁ = R ± ΔR₁
R₂ = R₂ ± ΔR₂
R = R ± ΔR
R_g = R_g ± ΔR_g
DR
Tol = _R
(4)
By developing the equations and neglecting the second order, the worst case is when the tolerances add up.
This is shown by Equation 5.
V_OUT
=
±
(4
Tol)
R
R_g
+ R_g
´ V_BAT
æ
+ _èçç1 ±
2
æ
Tol _èçç 1 +
2R
R + R_g
ö
ø÷÷
ö
÷
ø÷
R_g
R
´ R_S
´ I_LOAD
where
• Tol = 0.01 for 1%
• Tol = 0.001 for 0.1%
(5)
If the resistors are perfectly matched, then Tol = 0 and V_OUT is calculated using Equation 6.
V_OUT
=
R_g
R
´ R_S
´ I_LOAD
(6)
The highest error is from the common mode, as shown in Equation 7.
4
(Tol) ^Rg
R + R_g
´
V_BAT
(7)
Gain of 10, R_g / R = 10, and Tol = 1%:
Common mode error = ((4 × 0.01) / 1.1) × 12 V = 0.436 V
Gain of 10 and Tol = 0.1%:
Common mode error = 43.6 mV
The resistors were chosen from 2% batches.
R₁ and R 12 kΩ
R₂ and R_g 120 kΩ
Ideal Gain = 120 / 12 = 10
The measured value of the resistors:
R₁ = 11.835 kΩ
R = 11.85 kΩ
R₂ = 117.92 kΩ
R_g = 118.07 kΩ
22
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