OPA1652_16 Datasheet, PDF (22/42 Pages) Texas Instruments – Audio Operational Amplifiers

OPA1652, OPA1654
SBOS477A – DECEMBER 2011 – REVISED AUGUST 2016
www.ti.com
Typical Application (continued)
e_NR
d
e_OA
3
(3)
To calculate the required resistor values, Equation 3 is inserted into Equation 2, and the resulting equation is
rearranged to solve for the parallel combination of R₁ and R₂ as shown in Equation 4. Using a value of 3.8
nV/√Hz as the broadband voltage noise of the OPA1652 results in a value of 96.8 Ω for the parallel combination
of R₁ and R₂. Standard value 200-Ω resistors were used for R₁ and R₂, resulting in a parallel value of 100 Ω,
which is suitably close to the required value.
2
R₁||R₂
d
e_OA2
36kT
d
3.8 nV/ Hz
36×1.381×10^-23×300
d
96.8
(4)
Because of the extremely wide bandwidth and high slew rate of the BUF634, no additional components were
required to maintain stability in the circuit or prevent latch-up conditions. This circuit was found to be stable with
capacitive loads over 1 nF, which is suitable for headphone applications.
8.2.3 Application Curves
The measured performance of the circuit is shown in Figure 42 through Figure 46. The frequency response is
extremely flat over the full audio bandwidth, deviating only 0.004 dB over the audible range. The decrease in
gain shown at low frequency is a result of the test equipment and not the amplifier circuit. The amplifier output
impedance, calculated from the change in gain in the loaded and unloaded conditions, is 0.036 Ω. The maximum
output power before clipping is displayed in Figure 43. For a 32-Ω load, the power amplifier was able to deliver
781 mW before clipping. The best THD+N performance achieved with a 32-Ω load was –117.2 dB at 678 mW (1
kHz, 22-kHz measurement bandwidth). THD+N vs frequency is shown in Figure 44 for a 2-V_RMS output level
measured in a 90-kHz bandwidth. The worst-case measurement was for a 16-Ω load (250 mW), 20-kHz input
frequency, –91.8 dB (0.0026%). Two FFTs are also shown of the amplifier output spectrum for a 2-V_RMS, 1-kHz,
fundamental into two different loads. All distortion harmonics are below –120 dB relative to the fundamental for
both loading conditions.
6.2
6.15
6.1
6.05
6
5.95
5.9
5.85
5.8
10
100
1k
Frequency (Hz)
No Load
32- Load
10k
C005
Figure 42. Amplifier Transfer Function
±60
0.1
±70
±80
0.01
±90
±100
0.001
±110
±120
16- Load
32- Load
0.0001
±130
128- Load
±140
250- Load
0.00001
0.001
0.01
0.1
1
10
Output Voltage (V_RMS)
C007
22-kHz measurement bandwidth, 1-kHz output
Figure 43. THD+N vs Frequency for Various Loads
22
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