AD8601/AD8602/AD8604
Voltage drop is created across the 0.1 Ω resistor that is
proportional to the load current. This voltage appears at the
inverting input of the amplifier due to the feedback correction
around the op amp. This creates a current through R1, which
in turn, pulls current through R2. For the low side monitor, the
monitor output voltage is given by
Figure 60 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 DAC 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.
R
⎡
⎤
⎛
⎜
⎝
⎞
⎟
⎠
SENSE
Monitor Output = 3V − R2×
× I
(2)
L
⎢
⎥
R1
⎣
⎦
3V
For the high side monitor, the monitor output voltage is
1µF
R
⎛
⎜
⎝
⎞
⎟
⎠
SENSE
V
4
3
OUT
0V TO 3V
Monitor Output = R2×
× I
L
(3)
5
2
1
4
5
6
R1
3-WIRE
SERIAL
INTERFACE
1
AD5320
R
AD8601
L
Using the components shown, the monitor output transfer
function is 2.5 V/A.
Figure 60. Using the AD8601 as a DAC Output Buffer to Drive Heavy Loads
USING THE AD8601 IN SINGLE-SUPPLY, MIXED
SIGNAL APPLICATIONS
The AD8601, AD7476, and AD5320 are all available in space-
saving SOT-23 packages.
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 that the ADCs or DACs 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.
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. Figure 38 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 59 shows the AD8601 used as an input buffer amplifier
to the AD7476, a 12-bit, 1 MSPS ADC. As with most ADCs,
total harmonic distortion (THD) increases with higher source
impedances. By using the AD8601 in a buffer configuration, 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 attenua-
tion up to 500 kHz, which is the maximum Nyquist frequency
for the AD7476.
Figure 61 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.
5V
5V
REF193
SUPPLY
V
V
25
29
35
1µF
TANT
DD
DD
5V
0.1µF 10µF
0.1µF
680nF
C1
100µF
R4
20Ω
2
3
8
1
A
4
3
V
5
2
SCLK
SDATA
CS
LEFT
OUT
DD
R2
2kΩ
4
1
V
R
IN
S
µC/µP
AD1881
(AC’97)
AD8602
GND
C2
100µF
AD7476/AD7477
R5
20Ω
AD8601
5
6
36
26
RIGHT
OUT
7
SERIAL
INTERFACE
B
V
R3
SS
2kΩ
Figure 59. A Complete 3 V 12-Bit 1 MHz Analog-to-Digital Conversion System
AD8602
NOTES
1. ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 61. A PC100-Compliant Line Output Amplifier
Rev. G | Page 17 of 24
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