OPA4830IPW Datasheet, PDF (23/45 Pages) Texas Instruments – Quad, Low-Power, Single-Supply, Wideband Operational Amplifier

OPA4830
www.ti.com.................................................................................................................................................... SBOS350A – DECEMBER 2006 – REVISED MAY 2008
Figure 74 illustrates the dc-coupled, gain of +2V/V,
dual power-supply circuit configuration used as the
basis of the ±5V Electrical Characteristics and Typical
Characteristics. For test purposes, the input
impedance is set to 50Ω with a resistor to ground and
the output impedance is set to 150Ω with a series
output resistor. Voltage swings reported in the
specifications are taken directly at the input and
output pins. For the circuit of Figure 74, the total
effective load is 150Ω 1.5kΩ. Two optional
components are included in Figure 74. An additional
resistor (348Ω) is included in series with the
noninverting input. Combined with the 25Ω dc source
resistance looking back towards the signal generator,
this gives an input bias current cancelling resistance
that matches the 375Ω source resistance seen at the
inverting input (see the DC Accuracy and Offset
Control section). In addition to the usual power-supply
decoupling capacitors to ground, a 0.01µF capacitor
is included between the two power-supply pins. In
practical printed circuit board layouts, this optional
capacitor typically improves the 2nd-harmonic
distortion performance by 3dB to 6dB.
50W Source
V_IN
348W
50W
+5V
0.1mF
6.8mF
+
1/4
OPA4830
V_O
150W
DC LEVEL-SHIFTING
Figure 75 shows a DC-coupled noninverting amplifier
that level-shifts the input up to accommodate the
desired output voltage range. Given the desired
signal gain (G), and the amount V_OUT needs to be
shifted up (ΔV_OUT) when V_IN is at the center of its
range, Equation 1 and Equation 2 give the resistor
values that produce the desired performance.
Assume that R₄ is between 200Ω and 1.5kΩ.
NG = G + V_OUT/V_S
R₁ = R₄/G
R₂ = R₄/(NG - G)
R₃ = R₄/(NG - 1)
(1)
where:
NG = 1 + R₄/R₃
V_OUT = (G)V_IN + (NG - G)V_S
(2)
Make sure that V_IN and V_OUT stay within the specified
input and output voltage ranges.
+V_S
R₂
R₁
V_IN
1/4
OPA4830
V_OUT
0.01mF
R_F
750W
R₃
R₄
R_G
750W
6.8mF
+
0.1mF
-5V
Figure 74. DC-Coupled, G = +2V/V, Bipolar Supply
Specification and Test Circuit
Figure 75. DC Level-Shifting
The circuit on the front page is a good example of
this type of application. It was designed to take V_IN
between 0V and 0.5V and produce V_OUT between 1V
and 2V when using a +3V supply. This output means
G = 2.00, and ΔV_OUT = 1.50V – G × 0.25V = 1.00V.
Plugging these values into Equation 1 and Equation 2
(with R₄ = 750Ω) gives: NG = 2.33, R₁ = 375Ω, R₂ =
2.25kΩ, and R₃ = 563Ω. The resistors were changed
to the nearest standard values for the front page
circuit.
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