OPA2836-Q1 Datasheet, PDF (34/44 Pages) Texas Instruments – Very-Low Power, Rail-to-Rail Out, Negative-Rail In, Voltage-Feedback Operational Amplifier

OPA2836-Q1
SBOS794 – DECEMBER 2016
www.ti.com
9.2 Typical Applications
9.2.1 Audio-Frequency Performance
The OPA2836-Q1 provides excellent audio performance with very low quiescent power. To show performance in
the audio band, a 2700 series audio analyzer from Audio Precision is used to test THD+N and FFT at 1-V_RMS
output voltage.
Figure 71 shows the test circuit used for the audio-frequency performance application.
V_IN
From AP
+2.5 V
V_OUT
To AP
100 pF ^OPA2836-Q1
10 W
-2.5 V
Copyright © 2016, Texas Instruments Incorporated
The 100-pF capacitor to ground on the input helped to decouple noise pick up in the lab and improved noise
performance.
Figure 71. OPA2836-Q1 Audio Precision Analyzer Test Circuit
9.2.1.1 Design Requirements
Design a low distortion, single-ended input to single-ended output audio amplifier using the OPA2836-Q1. The
2700 series audio analyzer from Audio Precision is used as the signal source and also as the measurement
system.
CONFIGURATION
OPA2836-Q1 unity-gain configuration
Table 4. Design Requirements
INPUT
EXCITATION
PERFORMANCE
TARGET
1-kHz tone frequency
> 110 dBc SFDR
R_Load
300 Ω and
100 kΩ
9.2.1.2 Detailed Design Procedure
The OPA2836-Q1 is tested in this application in a unity-gain buffer configuration. A buffer configuration is chosen
because this configuration maximizes the loop gain of the amplifier configuration. At higher closed-loop gains, the
loop gain of the circuit reduces, resulting in degraded harmonic distortion. The relationship between distortion
and closed-loop gain at a fixed input frequency is illustrated in Figure 35 in the Typical Characteristics section.
The test was performed under varying output load conditions using a resistive load of 300 Ω and 100 kΩ.
Figure 33 illustrates the distortion performance of the amplifier versus output resistive load. Output loading,
output swing, and closed-loop gain play a key role in determining the distortion performance of the amplifier.
NOTE
The 100-pF capacitor to ground on the input helped to decouple noise pickup in the lab
and improved noise performance.
The Audio Precision was configured as a single-ended output in this application circuit. In applications where a
differential output is available, the OPA2836-Q1 device can be configured as a differential-to-single-ended
amplifier; see Figure 65. Power-supply bypassing is critical in order to reject noise from the power supplies. A
2.2-μF power-supply decoupling capacitor must be placed within 2 inches of the device and can be shared with
other operational amplifiers on the same board. A 0.1-μF power supply decoupling capacitor must be placed as
close to the power supply pins as possible, preferably within 0.1 inch. For split supply, a capacitor is required for
both supplies. A 0.1-µF capacitor placed directly between the supplies is also beneficial for improving system
noise performance. If the output load is very heavy, in the order of 16 Ω to 32 Ω, performance of the amplifier
can begin to degrade. In order to drive such heavy loads, both channels of the OPA2836-Q1 device can be
paralleled with the outputs isolated with 1-Ω resistors to reduce the loading effects.
34
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