AD8531A Analog Devices, AD8531A Datasheet - Page 12

• Manufacturer Part Number: AD8531A
• Description: Low Cost, 250 ma Output Single-supply Amplifiers
• Manufacturer: Analog Devices

AD8531/AD8532/AD8534
A Single-Supply Headphone Amplifier
Because of its speed and large output drive, the AD8531/AD8532/
AD8534 makes for 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 sup-
ply. To insure maximum signal swing available to drive the
headphone, the amplifier inputs are biased to V+/2, which is in
this case 2.5 V. The 100 k resistor to the positive supply is
equally split into two 50 k resistors with their common point
bypassed by 10 F to prevent power supply noise from contami-
nating the audio signal.
The audio signal is then ac-coupled to each input through a
10 F 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, then the ac coupling and biasing resistors are
not required. A 270 F 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
headphones, which can range from 32
tional 16
protect the op amp’s output stage by limiting capacitor dis-
charge current. When driving a 48
less than 0.3% THD+N at output drive levels of 4 V p-p.
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, and
the ease of controlling low/high channel drive, plus the controlled
driver damping provided by a dedicated amplifier. Both Sallen-
Key (SK) and multiple-feedback (MFB) filter architectures are
useful 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 lev-
els of 1.4 V rms using general purpose unity-gain HP/LP stages.
RIGHT
INPUT
INPUT
LEFT
Figure 40. A Single-Supply, Stereo Headphone Driver
10µF
10µF
50k
50k
50k
50k
resistor is used in series with the output capacitor to
+V + 5V
+V
100k
100k
10µF
10µF
AD8532
AD8532
+V + 5V
1/2
1/2
1µF/0.1µF
16
16
load, the circuit exhibits
to 600 . An addi-
270µF
270µF
50k
50k
HEADPHONE
HEADPHONE
RIGHT
LEFT
–12–
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.
The crossover example frequency of 500 Hz can be shifted
lower or higher by frequency scaling of either resistors or ca-
pacitors. 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.
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.
TO U1
Figure 41. A Single-Supply, Two-Way Active Crossover
V
IN
+V
100k
S
R
Crossover
Frequency (Hz)
100
200
319
500
1 k
2 k
5 k
10 k
NOTES
Applicable for filter
1
2
Table II. RC Component Selection for Various
Crossover Frequencies
IN
For Sallen-Key stage U1A: R1 = R2, and C1 = C2, etc.
For Multiple Feedback stage U1B: R6 = R5, R7 = R5/2, and
C4 = 2C3.
10µF
0.1µF
C
IN
100k
100k
0.01µF
31.6k
31.6k
+V
C1
R5
100µF/25V
S
R2
= 2.
C2
0.01µF
10µF
15.8k
C4
0.02µF
COM
+5V
R7
31.6k
31.6k
R1
R6
3
2
6
5
+V
S
4
U1A
AD8532
0.01µF
U1B
AD8532
R1/C1 (U1A)
R5/C3 (U1B)
160 k /0.01 F
80.6 k /0.01 F
49.9 k /0.01 F
31.6 k /0.01 F
16 k /0.01 F
8.06 k /0.01 F
3.16 k /0.01 F
1.6 k /0.01 F
C3
1
7
49.9
49.9
R3
R4
270µF
270µF
+
+
1
2
REV. 0
100k
100k
AND UP
500Hz
DC –
500Hz
LO
HI