Texas Instruments SoundPlus OPA1622EVM User manual

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OPA1622EVM SoundPlus™ Audio Operational Amplifier Evaluation Module
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All other trademarks are the property of their respective owners.
User's Guide
SBOU172–September 2016
OPA1622EVM SoundPlus™ Audio Operational Amplifier
Evaluation Module
This user's guide contains information for the OPA1622 as well as support documentation for the
OPA1622 evaluation module (EVM). Included are the performance specifications, set-up procedure,
modifications, measured data, printed circuit board (PCB) layout, schematic, and bill of materials (BOM) of
the OPA1622EVM.
Contents
1 Introduction ................................................................................................................... 2
2 Performance Specification Summary ..................................................................................... 2
3 Modifications.................................................................................................................. 3
3.1 Gain................................................................................................................... 3
3.2 Cutoff Frequency.................................................................................................... 4
3.3 Phase Shift .......................................................................................................... 4
4 Test Setup and Results..................................................................................................... 4
4.1 Power Supply Connections........................................................................................ 5
4.2 Input Connections .................................................................................................. 5
4.3 Output Connections ................................................................................................ 5
4.4 Enable ............................................................................................................... 5
4.5 THD+N vs. Frequency ............................................................................................. 6
4.6 THD+N vs. Amplitude .............................................................................................. 7
4.7 Fast Fourier Transforms ........................................................................................... 8
5 Board Layout................................................................................................................ 10
5.1 Layout............................................................................................................... 10
6 Schematic, Bill of Materials, and Reference............................................................................ 12
6.1 Schematic .......................................................................................................... 12
6.2 Bill of Materials .................................................................................................... 13

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6.3 Reference .......................................................................................................... 13
List of Figures
1 OPA1622EVM Schematic .................................................................................................. 3
2 Power Supply Connections................................................................................................. 5
3 THD+N vs. Frequency for a 32-ΩLoad .................................................................................. 6
4 THD+N vs. Frequency for a 16-ΩLoad................................................................................... 6
5 THD+N vs. Amplitude for a 32-ΩLoad ................................................................................... 7
6 THD+N vs. Amplitude for a 16-ΩLoad ................................................................................... 7
7 FFT of Left Channel With a 32-ΩLoad................................................................................... 8
8 FFT of Right Channel with a 32-ΩLoad.................................................................................. 8
9 FFT of Left Channel With a 16-ΩLoad................................................................................... 9
10 FFT of Right Channel With a 16-ΩLoad ................................................................................. 9
11 Top Layer PCB Layout .................................................................................................... 10
12 Bottom Layer PCB Layout ................................................................................................ 11
13 OPA1622EVM Schematic................................................................................................. 12
List of Tables
1 OPA1622EVM Measured Performance Summary ...................................................................... 2
2 OPA1622EVM Bill of Materials........................................................................................... 13
1 Introduction
The OPA1622 is a high-performance, bipolar-input SoundPlus™ audio operational amplifier. For a full list
of electrical characteristics of the OPA1622, please refer to the OPA1622 product datasheet (SBOS727).
2 Performance Specification Summary
A summary of the OPA1622EVM performance specifications is provided in Table 1. Specifications are
given for a supply voltage of Vs= ±5 V and at an ambient temperature of 25°C, unless otherwise noted.
Table 1. OPA1622EVM Measured Performance Summary
Specification Test Conditions Measured Performance
Total Harmonic Distortion Plus Noise
(THD+N) at 1 kHz VIN = 1 Vrms, Load = 32 Ω, Measurement Bandwidth = 90 kHz –108.10 dB
THD+N vs. at 1 kHz VIN = 1 Vrms, Load = 16 Ω, Measurement Bandwidth
= 90 kHz –107.8 dB
Second Harmonic – Left Channel VIN = 1 Vrms, Load = 32 Ω, Fin = 1 kHz –125.45 dBV
Second Harmonic – Right Channel VIN = 1 Vrms, Load = 32 Ω, Fin = 1 kHz –126.90 dBV
Second Harmonic – Left Channel VIN = 1 Vrms, Load = 16 Ω, Fin = 1 kHz –120.25 dBV
Second Harmonic – Right Channel VIN = 1 Vrms, Load = 16 Ω, Fin = 1 kHz –120.68 dBV

6
Right Channel
5
R
Gain R =
2
Left Channel
1
R
Gain
R
=
( )
2
Left ChannelOutput Right Channel Output
1
R
V V (IN ) (IN )
R
= = ´ + - -
8 6 6
Right Channel Output
7 8 5
R R R
V 1 (IN ) (IN )
R R R R5
æ ö æ ö
= ´ + ´ + - ´ -
ç ÷ ç ÷
+è ø
è ø
4 2 2
Left ChannelOutput
3 4 1 1
R R R
V 1 (IN ) (IN )
R R R R
æ ö æ ö
= ´ + ´ + - ´ -
ç ÷ ç ÷
+è ø è ø
Left Channel Output
(Right Channel Output)
R1 (R5) R2 (R6)
R3 (R7)
R4
(R8)
C1 (C3)
C2
(C4)
OPA1622
IN>
IN+
Left Channel Input
(Right Channel Input)
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OPA1622EVM SoundPlus™ Audio Operational Amplifier Evaluation Module
3 Modifications
This EVM is designed to provide access to the features of and measure the performance of the OPA1622.
Modifications of the OPA1622EVM can be made and include; adjusting the gain, phase shift, and cut-off
frequency. The schematic of the OPA1622EVM is displayed in Figure 1. For a full schematic of the
OPA1622EVM, see Figure 13.
Figure 1. OPA1622EVM Schematic
3.1 Gain
Equation 1 and Equation 2 display the transfer function of the circuit shown in Figure 1.
(1)
(2)
Most applications require the left and right channel to be balanced. Balancing the outputs is accomplished
by setting R2 = R4 = R6 = R8 and R1 = R3 = R5 = R7. This simplifies Equation 1 and Equation 2 into
Equation 3.
(3)
If the channels require unbalanced gain, the gain of each channel can be calculated using Equation 4 and
Equation 5.
given
• R2= R4and R1= R3(4)
given
• R6= R8and R5= R7(5)

1
c
tan-æ ö Q = - ç ÷
è ø
f
f
c right
6 3
1
2 R C
-=
p ´ ´
f
c left
2 1
1
2 R C
-=
p ´ ´
f
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3.2 Cutoff Frequency
This EVM provides the ability to filter the output of the OPA1622. The cutoff frequency of the filter can be
calculated using Equation 6 and Equation 7.
given
• R2= R4, R1= R3, and C1= C2(6)
given
• R6= R8, R5= R7, and C3= C4(7)
3.3 Phase Shift
The phase shift, θ, is calculated using Equation 8.
where
• ƒ is the maximum frequency of interest within the audio band
• ƒcis the cutoff frequency discussed in Section 3.2 (8)
4 Test Setup and Results
This section describes how to properly connect, set up, and use the OPA1622EVM. This section also
includes measured data of the OPA1622EVM to display typical performance of the OPA1622EVM.
Measurements include:
•THD+N vs. Frequency for a 32- and 16-Ωload
•THD+N vs. Amplitude for a 32- and 16-Ωload
•Fast-Fourier Transform (FFT) for a 32- and 16-Ωload
The THD+N vs. Frequency,THD+N vs. Amplitude, and FFT measurements were taken using an Audio
Precision APx555. All measurements were taken using ±5-V supplies at an ambient temperature of 25 °C,
unless otherwise noted.

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4.1 Power Supply Connections
The power supply connections for the OPA1622EVM are provided through the use of connector J4
located at the top of the EVM. The positive power supply connection is labeled VCC, the negative power
supply connection is labeled VEE, and the ground connection is labeled GND. To connect power to the
OPA1622EVM, insert wires into each terminal of J4 and then tighten the screws to make the connection.
Figure 2 displays the proper way to connect power to the OPA1622EVM. For the minimum and maximum
supply voltages of the OPA1622EVM, please refer to the OPA1622 product datasheet (SBOS727).
Figure 2. Power Supply Connections
4.2 Input Connections
Signals for the left channel and right channel input are applied to the OPA1622EVM through the use of
connectors J1 and J3, respectively. Connect wires to J1 and J3 to provide an input signal from a source
such as an audio analyzer or audio digital-to-analog converter (DAC). The positive input from the source
connects to the pin labeled IN+ (upper pin), the negative input from the source connects to the pin labeled
IN– (lower pin), and the ground connection from the source connects to the center pin of J1 and J3.
4.3 Output Connections
Output connections are provided through the use of the audio jack, J2, and two test points labeled Left
Channel and Right Channel near the bottom of the OPA1622EVM. The audio jack provides a way to
connect headphones or a resistive load to the output of the OPA1622 while testing the performance of the
OPA1622EVM. Test points labeled Left Channel and Right Channel provide a connection to measure the
performance of the left and right channels of the OPA1622EVM.
4.4 Enable
Jumper J5 provides access to the enable pin of the OPA1622. Placing a shunt across J5 disables the
OPA1622 by grounding the enable pin. When the enable pin is grounded, a current will flow through R9 to
ground which is much larger than the shutdown current of the OPA1622. Removing the shunt across J5
enables the OPA1622 by pulling the enable pin up to VCC through resistor R9. Note that voltages up to
VCC can be applied to the enable pin of the OPA1622. External sources can be applied to the enable pin
by removing the shunt and resistor R9 and connecting an external source to the pin of J5 labeled EN.

-140
-120
-100
-80
-60
0.00001
0.0001
0.001
0.01
0.1
20 200 2000 20000
Total Harmonic Distortion + Noise (dB)
Total Harmonic Distortion + Noise (%)
Frequency (Hz)
Left Channel
Right Channel
C002
-140
-120
-100
-80
-60
0.00001
0.0001
0.001
0.01
0.1
20 200 2000 20000
Total Harmonic Distortion + Noise (dB)
Total Harmonic Distortion + Noise (%)
Frequency (Hz)
Left Channel
Right Channel
C001
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4.5 THD+N vs. Frequency
For all THD+N vs. Frequency measurements, the input signal frequency was swept from 20 Hz to 20 kHz
and had an amplitude of 1 Vrms on the output of the OPA1622 with the measurement bandwidth of the
Audio Precision set to 90 kHz. A small variation in the THD+N performance between amplifier channels is
normal. Figure 3 shows the THD+N vs. Frequency for a 32-Ωload.
Figure 3. THD+N vs. Frequency for a 32-ΩLoad
Figure 4 shows the THD+N vs. Frequency for a 16-Ωload.
Figure 4. THD+N vs. Frequency for a 16-ΩLoad

-140
-120
-100
-80
-60
0.00001
0.0001
0.001
0.01
0.1
0.01 0.1 1
Total Harmonic Distortion + Noise (dB)
Total Harmonic Distortion + Noise (%)
Frequency (Vrms)
Left Channel
Right Channel
C004
-140
-120
-100
-80
-60
0.00001
0.0001
0.001
0.01
0.1
0.01 0.1 1
Total Harmonic Distortion + Noise (dB)
Total Harmonic Distortion + Noise (%)
Frequency (Vrms)
Left Channel
Right Channel
C003
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4.6 THD+N vs. Amplitude
For all THD+N vs. Amplitude measurements, the output amplitude was swept from 10 mVrms to 3 Vrms at
a frequency of 1 kHz. The measurement bandwidth of the Audio Precision was set to 22 kHz. Note that
power supply voltages larger than ±5 V may cause the output of the OPA1622 to clip at a lower output
amplitude than what is shown in the measurements because the increased power dissipation in the
amplifier will trigger the thermal protection circuitry. See the OPA1622 product datasheet (SBOS727),
Applications section for information on calculating power dissipation. Figure 5 shows the THD+N vs.
Amplitude for a 32-Ωload.
Figure 5. THD+N vs. Amplitude for a 32-ΩLoad
Figure 6 shows the THD+N vs. Amplitude for a 16-Ωload.
Figure 6. THD+N vs. Amplitude for a 16-ΩLoad

-180
-160
-140
-120
-100
-80
-60
-40
-20
0
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Amplitude (dBV)
Frequency (Hz)
C006
íG%96HFRQG+DUPRQLF
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Amplitude (dBV)
Frequency (Hz)
C005
íG%96HFRQG+DUPRQLF
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4.7 Fast Fourier Transforms
For all FFT measurements, a frequency of 1 kHz and amplitude of 1 Vrms on the output was used. The 1
Vrms fundamental corresponds to 0 dBV in all FFT measurements. Figure 7 shows an FFT of the left
channel with a 32-Ωload. The second harmonic was measured to be –125.45 dBV.
Figure 7. FFT of Left Channel With a 32-ΩLoad
Figure 8 shows an FFT of the right channel with a 32-Ωload. The second harmonic was measured to be
–126.90 dBV.
Figure 8. FFT of Right Channel with a 32-ΩLoad

-180
-160
-140
-120
-100
-80
-60
-40
-20
0
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Amplitude (dBV)
Frequency (Hz)
C008
í dBV (Second Harmonic)
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Amplitude (dBV)
Frequency (Hz)
C007
í dBV (Second Harmonic)
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Figure 9 shows an FFT of the left channel with a 16-Ωload. The second harmonic was measured to be
–120.25 dBV.
Figure 9. FFT of Left Channel With a 16-ΩLoad
Figure 10 shows an FFT of the right channel with a 16-Ωload. The second harmonic was measured to be
–120.68 dBV.
Figure 10. FFT of Right Channel With a 16-ΩLoad

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5 Board Layout
This section provides a description of the OPA1622EVM board layout and layer illustrations.
5.1 Layout
The board layout for the OPA1622EVM is shown in Figure 11 and Figure 12. The top layer consists of all
signal traces and is poured with a solid ground plane. The traces of the positive input (IN+) and negative
input (IN–) for both the left and right channel were kept as balanced as possible to eliminate any
impedance mismatch due to trace impedance. The decoupling capacitors, C5 and C6, were positioned as
close as possible to the power supply pins of the device. Vias were placed at the ground connection of
every component to provide a low impedance path on the bottom layer back to the supply ground. It is
important to provide a very clean, low impedance return path for the audio jack (J2); therefore multiple
stitching vias were placed around the ground connection of the audio jack. Also, the connection to the
thermal pad of the OPA1622 on the bottom layer was kept to a minimum to ensure currents from the
audio jack ground to the supply ground have a clean return path. Note that due to the size of the copper
pour for the thermal pad on the bottom layer, the thermal performance specified in the OPA1622
datasheet may not be met on the OPA1622EVM. Refer to the application report, PowerPAD™ Thermally
Enhanced Package (SLMA002), for more information.
Figure 11. Top Layer PCB Layout