OPA4277-EP Datasheet, PDF (12/20 Pages) Texas Instruments – OPA4277-EP High Precision Operational Amplifier

OPA4277-EP
SBOS714 – NOVEMBER 2014
www.ti.com
8.2.2.2 Input Protection
The inputs of the OPA4277 are protected with 1-kΩ series input resistors and diode clamps. The inputs can
withstand ±30-V differential inputs without damage. The protection diodes conduct current when the inputs are
overdriven. This may disturb the slewing behavior of unity-gain follower applications, but will not damage the
operational amplifier.
8.2.2.3 Input Bias Current Cancellation
The input stage base current of the OPA4277 is internally compensated with an equal and opposite cancellation
circuit. The resulting input bias current is the difference between the input stage base current and the
cancellation current. This residual input bias current can be positive or negative.
When the bias current is canceled in this manner, the input bias current and input offset current are
approximately the same magnitude. As a result, it is not necessary to use a bias current cancellation resistor, as
is often done with other operational amplifiers (see Figure 23). A resistor added to cancel input bias current
errors may actually increase offset voltage and noise.
R₂
R₂
R₁
R₁
Op Amp
OPA4277
R_B = R₂ || R₁
No bias current
cancellation resistor
(see text)
(a)
Conventional op amp with external bias
current cancellation resistor.
(b)
OPA4277 with no external bias current
cancellation resistor.
Figure 23. Input Bias Current Cancellation
V+
1/2
OPA4277
R–∆R
V₁
Load
Cell
R+∆R
V₂
R+∆R
R–∆R
R₂
V–
V+
1/2
OPA4277
V–
R₁
V_OUT = (V₁ –
V₂)(1
+
R₂
R₁
)
R₂
R₁
For integrated solution see: INA126, INA2126 (dual)
INA125 (on-board reference)
INA122 (single-supply)
Figure 24. Load Cell Amplifier
12
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