LME49721MAX Datasheet, PDF (15/29 Pages) Texas Instruments – LME49721 High-Performance, High-Fidelity Rail-to-Rail Input/Output Audio Operational Amplifier

LME49721
www.ti.com
SNAS371C – SEPTEMBER 2007 – REVISED APRIL 2013
APPLICATION INFORMATION
DISTORTION MEASUREMENTS
The vanishingly low residual distortion produced by LME49721 is below the capabilities of all commercially
available equipment. This makes distortion measurements just slightly more difficult than simply connecting a
distortion meter to the amplifier's inputs and outputs. The solution. however, is quite simple: an additional
resistor. Adding this resistor extends the resolution of the distortion measurement equipment.
The LME49721's low residual is an input referred internal error. As shown in Figure 69, adding the 10Ω resistor
connected between a the amplifier's inverting and non-inverting inputs changes the amplifier's noise gain. The
result is that the error signal (distortion) is amplified by a factor of 101. Although the amplifier's closed-loop gain
is unaltered, the feedback available to correct distortion errors is reduced by 101. To ensure minimum effects on
distortion measurements, keep the value of R1 low as shown in Figure 69.
This technique is verified by duplicating the measurements with high closed-loop gain and/or making the
measurements at high frequencies. Doing so, produces distortion components that are within equipments
capabilities. This datasheet's THD+N and IMD values were generated using the above described circuit
connected to an Audio Precision System Two Cascade.
R₁
1 k:
R₂
1 k:
R₃
10:
Generator Output
-
LME49721
+
Audio Precision
System Two
Cascade
Distortion Signal Gain = 1 + (R2/R3)
Analyzer Input
Figure 69. THD+N and IMD Distortion Test Circuit with A_V = 2
OPERATING RATINGS AND BASIC DESIGN GUIDELINES
The LME49721 has a supply voltage range from +2.2V to +5.5V single supply or ±1.1 to ±2.75V dual supply.
Bypassed capacitors for the supplies should be placed as close to the amplifier as possible. This will help
minimize any inductance between the power supply and the supply pins. In addition to a 10μF capacitor, a 0.1μF
capacitor is also recommended in CMOS amplifiers.
The amplifier's inputs lead lengths should also be as short as possible. If the op amp does not have a bypass
capacitor, it may oscillate.
BASIC AMPLIFIER CONFIGURATIONS
The LME49721 may be operated with either a single supply or dual supplies. Figure 70 shows the typical
connection for a single supply inverting amplifier. The output voltage for a single supply amplifier will be centered
around the common-mode voltage Vcm. Note: the voltage applied to the Vcm insures the output stays above
ground. Typically, the Vcm should be equal to V_DD/2. This is done by putting a resistor divider ckt at this node,
see Figure 70.
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