AD8591/AD8592/AD8594

–9–

REV. A

In any application, the absolute maximum junction temperature

must be limited to +150

°C. If this junction temperature is ex-

ceeded, the device could suffer premature failure. If the output

voltage and output current are in phase, for example, with a

purely resistive load, the power dissipated by the AD859x can

be found as:

PI

V

V

ISS

SY

OUT

D

LOAD

=×

()

–

(4)

Where

By calculating the power dissipation of the device and using the

thermal resistance value for a given package type, the maximum

allowable ambient temperature for an application can be found

using Equation 3.

Capacitive Loading

The AD859x exhibits excellent capacitive load driving capabilities

and can drive up to 10 nF directly. Although the device is stable

with large capacitive loads, there is a decrease in amplifier band-

width as the capacitive load increases. Figure 31 shows a graph of

the AD8592 unity gain bandwidth under various capacitive loads.

CAPACITIVE LOAD – nF

4

3.5

0

0.01

100

0.1

110

2

1.5

1

0.5

3

2.5

Figure 31. Unity Gain Bandwidth vs. Capacitive Load

When driving heavy capacitive loads directly from the AD859x

output, a snubber network can be used to improve transient

response. This network consists of a series R-C connected from

the amplifier’s output to ground, placing it in parallel with the

capacitive load. The configuration is shown in Figure 32. Al-

though this network will not increase the bandwidth of the am-

plifier, it will significantly reduce the amount of overshoot, as

shown in Figure 33.

+5V

5

100mV p-p

AD8592

47nF

1 F

Figure 32. Configuration for Snubber Network to

Compensate for Capacitive Loads

10

0%

10 s

50mV

100

90

50mV

47nF LOAD

ONLY

SNUBBER

IN CIRCUIT

Figure 33. Snubber Network Reduces Overshoot and

Ringing Caused from Driving Heavy Capacitive Loads

The optimum values for the snubber network should be determined

empirically based on the size of the capacitive load. Table I shows a

few sample snubber network values for a given load capacitance.

Table I. Snubber Networks for Large Capacitive Loads

Load Capacitance

Snubber Network

0.47 nF

300

Ω, 0.1 µF

4.7 nF

30

Ω, 1 µF

47 nF

5

Ω, 1 µF

A PC-98 Compliant Headphone/Speaker Amplifier

Because of its high output current performance and shutdown

feature, the AD8592 makes an excellent amplifier for driving an

audio output jack in a computer application. Figure 34 shows

how the AD8592 can be interfaced with an AC97 codec to drive

headphones or speakers.

U1-A

R2

2k

4

C1

100 F

+5V

1

10

2

3

5

+5V

AD1881

(AC97)

R4

20

+5V

R1

100k

7

8

6

9

R5

20

C2

100 F

NOTE: ADDITIONAL PINS

OMITTED FOR CLARITY

U1-B

U1 = AD8592

R3

2k

NC

28

35

36

Figure 34. A PC-98 Compliant Headphone/Line Out Amplifier

When headphones are plugged into the jack, the normalizing con-

tacts disconnect from the audio contacts. This allows the voltage to

the AD8592 shutdown pins to be pulled up to +5 V, activating the

amplifiers. With no plug in the output jack, the shutdown voltage is

pulled to 100 mV through the R1 and R3 + R5 voltage divider.

This powers the AD8592 down when it is not needed, saving

current from the power supply or battery.