AD8602DRM Analog Devices, AD8602DRM Datasheet - Page 15

• Manufacturer Part Number: AD8602DRM
• Description: Precision CMOS Single Supply Rail-to-Rail Input/Output Wideband Operational Amplifiers
• Manufacturer: Analog Devices

Using the components shown, the monitor output transfer function
is 2.5 V/A.
Using the AD8601 in Single Supply Mixed-Signal Applications
Single supply mixed-signal applications requiring 10 or more bits of
resolution demand both a minimum of distortion and a maximum
range of voltage swing to optimize performance. To ensure the A/D
or D/A converters achieve their best performance an amplifier often
must be used for buffering or signal conditioning. The 750 µV
maximum offset voltage of the AD8601 allows the amplifier to be
used in 12-bit applications powered from a 3 V single supply, and
its rail-to-rail input and output ensure no signal clipping.
Figure 6 shows the AD8601 used as a input buffer amplifier to
the AD7476, a 12-bit 1 MHz A/D converter. As with most A/D
converters, total harmonic distortion (THD) increases with higher
source impedances. By using the AD8601 in a buffer configura-
tion, the low output impedance of the amplifier minimizes THD
while the high input impedance and low bias current of the op
amp minimizes errors due to source impedance. The 8 MHz
gain-bandwidth product of the AD8601 ensures no signal attenu-
ation up to 500 kHz, which is the maximum Nyquist frequency
for the AD7476.
Figure 7 demonstrates how the AD8601 can be used as an output
buffer for the DAC for driving heavy resistive loads. The AD5320
is a 12-bit D/A converter that can be used with clock frequencies
up to 30 MHz and signal frequencies up to 930 kHz. The rail-to-
rail output of the AD8601 allows it to swing within 100 mV of the
positive supply rail while sourcing 1 mA of current. The total
current drawn from the circuit is less than 1 mA, or 3 mW from
a 3 V single supply.
The AD8601, AD7476, and AD5320 are all available in space-
saving SOT-23 packages.
V
IN
INTERFACE
SERIAL
3-WIRE
R
S
Monitor Output V
4
3
2
1 F
5
4
5
6
AD8601
1
AD5320
680nF
3V
2
=
V
GND
V
1
DD
IN
AD7476/AD7477
TANT
+ −
1 F
(
R
3V
2
4
3
)
×
0.1 F
SDATA



REF193
SCLK
2
5
R
CS
SENSE
AD8601
R
1
10 F
INTERFACE
1
SERIAL
V
0V TO 3.0V

 ×

OUT
I
0.1 F
L
5V
SUPPLY
C/ P
R
L
(3)
PC100 Compliance for Computer Audio Applications
Because of its low distortion and rail-to-rail input and output, the
AD860x is an excellent choice for low cost, single supply audio
applications, ranging from microphone amplification to line output
buffering. TPC 34 shows the total harmonic distortion plus noise
(THD + N) figures for the AD860x. In unity gain, the amplifier
has a typical THD + N of 0.004%, or –86 dB, even with a load
resistance of 600 Ω. This is compliant with the PC100 specification
requirements for audio in both portable and desktop computers.
Figure 8 shows how an AD8602 can be interfaced with an AC’97
codec to drive the line output. Here, the AD8602 is used as a
unity-gain buffer from the left and right outputs of the AC’97
CODEC. The 100 µF output coupling capacitors block dc current
and the 20 Ω series resistors protect the amplifier from short-circuits
at the jack.
SPICE Model
The SPICE macro-model for the AD860x amplifier is available
and can be downloaded from the Analog Devices website at
http://www.analog.com. The model will accurately simulate a
number of both dc and ac parameters, including open-loop gain,
bandwidth, phase margin, input voltage range, output voltage
swing versus output current, slew rate, input voltage noise, CMRR,
PSRR, and supply current versus supply voltage. The model is
optimized for performance at 27°C. Although it will function at
different temperatures, it may lose accuracy with respect to the
actual behavior of the AD860x.
NOTE: ADDITIONAL PINS
OMITTED FOR CLARITY
RIGHT
AD1881
(AC97)
LEFT
V
V
OUT
V
OUT
DD
DD
SS
28
35
36
+5V
5
6
3
2
U1-A
U1-B
U1 = AD8602D
+5V
8
4
7
1
AD8601/AD8602
100 F
100 F
C1
C2
2k
2k
R2
R3
20
20
R4
R5