AD8644 Analog Devices, AD8644 Datasheet - Page 12

• Manufacturer Part Number: AD8644
• Description: 18 V Operational Amplifier (Quad)
• Manufacturer: Analog Devices

Specifications of AD8644

• -3db Bandwidth: 5.5MHz
• Slew Rate: 7.5V/µs
• Vos: 1mV
• Ib: 80nA
• # Opamps Per Pkg: 4
• Input Noise (nv/rthz): 12nV/rtHz
• Vcc-vee: 5V to 18V
• Isy Per Amplifier: 1.1mA
• Packages: SOIC,SOP

AD8614/AD8644
If gain is required from the output amplifier, four additional
resistors should be added as shown in Figure 31.
The gain of the AD8644 can be set as
Input coupling capacitors are not required for either circuit as
the reference voltage is supplied from the AD1881A.
The resistors R4 and R5 help protect the AD8644 output in case
the output jack or headphone wires are accidentally shorted to
ground. The output coupling capacitors C1 and C2 block dc
LINE_OUT_R
LINE_OUT_L
NOTES
1. ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 31. A PC-99-Compliant Headphone/Speaker Amplifier with Gain
AD1881A
(AC'97)
A
AV
AV
AV
VREF
V
DD1
DD2
SS1
=
R
R
38
35
27
36
26
25
6
5
10kΩ
10kΩ
R5
R5
5V
2
3
7
8
U1-A
5
6
U1-B
20kΩ
20kΩ
R6
R6
5V
A
10
4
V
=
9
R6
R5
U1 = AD8644
1
= +6dB WITH VALUES SHOWN
100µF
100µF
+
+
C2
C1
2kΩ
2kΩ
R1
R2
20Ω
20Ω
R3
R4
Rev. B | Page 12 of 16
current from the headphones and create a high-pass filter with a
corner frequency of
where R
The remaining two amplifiers can be used as low voltage
microphone preamplifiers. A single AD8614 can be used as a
standalone microphone preamplifier. Figure 32 shows this
implementation.
AD1881A
(AC'97)
VREF
MIC1
MIC2
f
−
3
L
dB
21
22
27
is the resistance of the headphones.
=
2
π
C1
Figure 32. Microphone Preamplifier
A
(
A
R4
V
V
1
10kΩ
10kΩ
= 20dB
= 20dB
+
R
L
)
1kΩ
1kΩ
+
+
1µF
1µF
5V
5V
2.2kΩ
2.2kΩ
MIC 1
MIC 2