AD8534AN(1999) Ver la hoja de datos (PDF) - Analog Devices
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AD8534AN Datasheet PDF : 16 Pages
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AD8531/AD8532/AD8534
A Single-Supply Headphone Amplifier
Because of its speed and large output drive, the AD8531/AD8532/
AD8534 makes an excellent headphone driver, as illustrated in
Figure 40. Its low supply operation and rail-to-rail inputs and
outputs give a maximum signal swing on a single +5 V supply.
To ensure maximum signal swing available to drive the head-
phone, the amplifier inputs are biased to V+/2, which in this
case is 2.5 V. The 100 kΩ resistor to the positive supply is
equally split into two 50 kΩ resistors, with their common point
bypassed by 10 µF to prevent power supply noise from contami-
nating the audio signal.
The audio signal is then ac-coupled to each input through a
10 µF capacitor. A large value is needed to ensure that the
20 Hz audio information is not blocked. If the input already has
the proper dc bias, the ac coupling and biasing resistors are not
required. A 270 µF capacitor is used at the output to couple the
amplifier to the headphone. This value is much larger than that
used for the input because of the low impedance of the head-
phones, which can range from 32 Ω to 600 Ω. An additional
16 Ω resistor is used in series with the output capacitor to pro-
tect the op amp’s output stage by limiting capacitor discharge
current. When driving a 48 Ω load, the circuit exhibits less than
0.3% THD+N at output drive levels of 4 V p-p.
+V + 5V
50k⍀
+V + 5V 1F/0.1F
LEFT
INPUT
50k⍀
10F
10F
100k⍀
1/2
AD8532
16⍀ 270F
50k⍀
LEFT
HEADPHONE
+V
50k⍀
RIGHT
INPUT
50k⍀
10F
10F
100k⍀
1/2
AD8532
16⍀ 270F
50k⍀
RIGHT
HEADPHONE
Figure 40. A Single-Supply, Stereo Headphone Driver
A Single-Supply, Two-Way Loudspeaker Crossover Network
Active filters are useful in loudspeaker crossover networks for
reasons of small size, relative freedom from parasitic effects, the
ease of controlling low/high channel drive and the controlled driver
damping provided by a dedicated amplifier. Both Sallen-Key
(SK) and multiple-feedback (MFB) filter architectures are use-
ful in implementing active crossover networks. The circuit
shown in Figure 41 is a single-supply, two-way active crossover
which combines the advantages of both filter topologies. This
active crossover exhibits less than 0.4% THD+N at output levels
of 1.4 V rms using general purpose unity-gain HP/LP stages.
In this two-way example, the LO signal is a dc-500 Hz
LP woofer output, and the HI signal is the HP (>500 Hz)
tweeter output. U1B forms an LP section at 500 Hz, while
U1A provides a HP section, covering frequencies ≥500 Hz.
VIN
RIN
100k⍀
C1
0.01F
R2
31.6k⍀
R1
31.6k⍀
C2
0.01F
+VS
U1A
AD8532
3
1
2
4
R3
49.9⍀
270F
+
500Hz
AND UP
HI
100k⍀
CIN
10F
R5
31.6k⍀
R6
31.6k⍀
+VS
100k⍀
100k⍀
R7
15.8k⍀
C4
6
0.02F
5
10F
C3
0.01F
R4
49.9⍀
270F
+
DC –
500Hz
LO
100k⍀
7
U1B
AD8532
+VS
TO U1
0.1F
+5V
100F/25V
COM
Figure 41. A Single-Supply, Two-Way Active Crossover
The crossover example frequency of 500 Hz can be shifted
lower or higher by frequency scaling of either resistors or
capacitors. In configuring the circuit for other frequencies,
complementary LP/HP action must be maintained between
sections, and component values within the sections must be in
the same ratio. Table II provides a design aid to adaptation,
with suggested standard component values for other frequencies.
Table II. RC Component Selection for Various
Crossover Frequencies
Crossover
Frequency (Hz)
100
200
319
500
1k
2k
5k
10 k
R1/C1 (U1A)1
R5/C3 (U1B)2
160 kΩ/0.01 µF
80.6 kΩ/0.01 µF
49.9 kΩ/0.01 µF
31.6 kΩ/0.01 µF
16 kΩ/0.01 µF
8.06 kΩ/0.01 µF
3.16 kΩ/0.01 µF
1.6 kΩ/0.01 µF
NOTES
Applicable for filter α = 2.
1For Sallen-Key stage U1A: R1 = R2, and C1 = C2, etc.
2For Multiple Feedback stage U1B: R6 = R5, R7 = R5/2, and
C4 = 2C3.
For additional information on the active filters and active cross-
over networks, please consult the data sheet for the OP279, a
dual rail-to-rail high-output current operational amplifier.
–12–
REV. B
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