AD8532_15 Datasheet, PDF (15/20 Pages) Analog Devices – Single-Supply Amplifiers

SINGLE-SUPPLY HEADPHONE AMPLIFIER
Because of its speed and large output drive, the AD8531/
AD8532/AD8534 make an excellent headphone driver, as
illustrated in Figure 44. 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 headphone, 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
contaminating 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 protect the
output stage of the op amp by limiting the 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
50kΩ
V 5V 1µF/0.1µF
LEFT
INPUT
50kΩ
10µF
10µF
100kΩ
1/2
AD8532
16Ω ^270µF
50kΩ
LEFT
HEADPHONE
V
50kΩ
RIGHT
INPUT
50kΩ
10µF
10µF
100kΩ
1/2
AD8532
16Ω ^270µF
50kΩ
RIGHT
HEADPHONE
Figure 44. Single-Supply, Stereo Headphone Driver
SINGLE-SUPPLY, 2-WAY LOUDSPEAKER
CROSSOVER NETWORK
Active filters are useful in loudspeaker crossover networks
because 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
useful in implementing active crossover networks. The circuit
shown in Figure 45 is a single-supply, 2-way active crossover
that combines the advantages of both filter topologies.
AD8531/AD8532/AD8534
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 2-way example, the LO signal is a dc-to-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 an HP
section, covering frequencies ≥500 Hz.
V_IN
R_IN
100kΩ
C1
0.01µF
R2
31.6kΩ
R1
31.6kΩ
C2
0.01µF
3
2
V_S
U1A
AD8532
R3
49.9Ω
270µF
+
1
4
500Hz
AND UP
HI
100kΩ
C_IN
10µF
R5
31.6kΩ
R6
31.6kΩ
V_S
100kΩ
100kΩ
R7
15.8kΩ
C4
6
0.02µF
5
10µF
C3
0.01µF
R4
49.9Ω
270µF
+
DC –
500Hz
LO
100kΩ
7
U1B
AD8532
V_S
TO U1
0.1µ F
5V
100µF/25V
COM
Figure 45. A Single-Supply, 2-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 6 provides a design aid to adaptation, with
suggested standard component values for other frequencies.
For additional information on the active filters and active crossover
networks, refer to the data sheet for the OP279, a dual rail-to-
rail, high output current, operational amplifier.
Table 6. RC Component Selection for Various Crossover
Frequencies¹
Crossover Frequency (Hz) R1/C1 (U1A)², R5/C3 (U1B)³
100
160 kΩ/0.01 μF
200
80.6 kΩ/0.01 μF
319
49.9 kΩ/0.01 μF
500
31.6 kΩ/0.01 μF
1k
16 kΩ/0.01 μF
2k
8.06 kΩ/0.01 μF
5k
3.16 kΩ/0.01 μF
10 k
1.6 kΩ/0.01 μF
1 _{Applicable for Filter A = 2.}
2 _{For Sallen-Key stage U1A: R1 = R2, and C1 = C2, and so on.}
3 _{For multiple feedback stage U1B: R6 = R5, R7 = R5/2, and C4 = 2C3.}
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