AD8591/AD8592/AD8594

Rev. B | Page 12 of 16

In any application, the absolute maximum junction temperature

must be limited to 150°C. If the junction temperature is exceeded,

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

(4)

where:

is the AD859x output load current.

is the AD859x supply voltage.

is the output voltage.

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 to 10 nF directly. Although the device is stable

with large capacitive loads, there is a decrease in amplifier

bandwidth as the capacitive load increases. Figure 35 shows

a graph of the AD8592 unity-gain bandwidth under various

capacitive loads.

4.0

3.5

0

0.01

0.1

110

2.0

1.5

1.0

0.5

3.0

2.5

100

CAPACITIVE LOAD (nF)

Figure 35. Unity-Gain Bandwidth vs. Capacitive Load

When driving heavy capacitive loads directly from the AD859x

output, a snubber network can be used to improve the transient

response. This network consists of a series RC connected from

the output of the amplifier to ground, placing it in parallel with

the capacitive load. The configuration is shown in Figure 36.

Although this network does not increase the bandwidth of the

amplifier, it significantly reduces the amount of overshoot, as

shown in Figure 37.

5Ω

AD8592

+5V

100mV p-p

1µF

47nF

Figure 36. Configuration for Snubber Network to Compensate for Capacitive Loads

47nF LOAD

ONLY

SNUBBER

IN CIRCUIT

50mV

50mV

10µs

Figure 37. Snubber Network Reduces Overshoot and Ringing

Caused by Driving Heavy Capacitive Loads

The optimum values for the snubber network should be

determined empirically based on the size of the capacitive load.

Table 5 shows a few sample snubber network values for a given

load capacitance.

Table 5. Snubber Networks for Large Capacitive Loads

Snubber Network

0.47

300

0.1

4.7

30

1

47

5

1

PC98-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 38 shows

how the AD8592 can be interfaced with an AC’97 codec to

drive headphones or speakers.

U1-A

4

C1

100µF

+5V

1

10

2

3

5

+5V

AD1881A*

(AC’97)

R4

20Ω

+5V

R1

100kΩ

7

8

6

9

R5

20Ω

C2

100µF

*ADDITIONAL PINS OMITTED FOR CLARITY.

U1-B

U1 = AD8592

NC

R2

2kΩ

R3

2kΩ

LINE_OUT_R

LINE_OUT_L

25

38

35

36

26

Figure 38. PC98-Compliant Headphone/Line Out Amplifier