Data Sheet

AD8601/AD8602/AD8604

Rev. I | Page 17 of 24

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













×













×

−

=

L

SENSE

I

R1

R

R2

V

Output

Monitor

3

(2)

For the high side monitor, the monitor output voltage is

L

SENSE

I

R1

R

R2

Output

Monitor

×













×

=

(3)

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 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.

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.

VDD

GND

SCLK

SDATA

VIN

CS

AD7476/AD7477

RS

AD8601

4

3

2

5

1

1µF

TANT

SERIAL

INTERFACE

5V

SUPPLY

0.1µF

0.1µF

10µF

680nF

REF193

µC/µP

Figure 59. A Complete 3 V 12-Bit 1 MHz Analog-to-Digital Conversion System

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.

AD8601

4

3

2

5

1

1

VOUT

0V TO 3V

3-WIRE

SERIAL

INTERFACE

RL

AD5320

4

5

6

3V

1µF

Figure 60. Using the AD8601 as a DAC Output Buffer to Drive Heavy Loads

The AD8601, AD7476, and AD5320 are all available in space-

saving SOT-23 packages.

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 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.

NOTES

1. ADDITIONAL PINS OMITTED FOR CLARITY.

2

3

4

8

1

VDD

VSS

VDD

LEFTOUT

RIGHTOUT

5V

5V

AD1881

(AC’97)

A

R4

20Ω

C1

100µF

R2

2kΩ

5

6

7

R5

20Ω

C2

100µF

R3

2kΩ

B

35

29

26

36

25

AD8602

AD8602

Figure 61. A PC100-Compliant Line Output Amplifier