AD8591/AD8592/AD8594
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
P
DISS
=
I
LOAD
× (
V
SY
−
V
OUT
)
50mV
47nF LOAD
ONLY
(4)
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.
50mV
10µs
Figure 37. Snubber Network Reduces Overshoot and Ringing
Caused by Driving Heavy Capacitive Loads
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
3.0
V
S
= ±2.5V
R
L
= 1kΩ
T
A
= 25°C
The optimum values for the snubber network should be
determined empirically based on the size of the capacitive load.
load capacitance.
Table 5. Snubber Networks for Large Capacitive Loads
Load Capacitance, C
L
(nF)
0.47
4.7
47
Snubber Network
R
S
(Ω)
C
S
(μF)
300
0.1
30
1
5
1
BANDWIDTH (MHz)
2.5
2.0
1.5
1.0
0.5
0
0.01
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.
+5V
01106-036
0.1
1
CAPACITIVE LOAD (nF)
10
100
AV
DD1 25
AV
DD2 38
LINE_OUT_L
35
2
+5V
10
C1
100µF
1
+5V
R1
100kΩ
R4
20Ω
R2 NC
2kΩ
Figure 35. Unity-Gain Bandwidth vs. Capacitive Load
U1-A
4
3
5
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.
+5V
AD1881A*
(AC’97)
6
LINE_OUT_R
36
AV
SS1 26
8
7
C2
100µF
U1-B
9
R3
2kΩ
01106-039
R5
20Ω
U1 = AD8592
R
S
5Ω
C
S
1µF
V
IN
100mV p-p
AD8592
V
OUT
*ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 38. PC98-Compliant Headphone/Line Out Amplifier
01106-037
C
L
47nF
Figure 36. Configuration for Snubber Network to Compensate for Capacitive Loads
Rev. B | Page 12 of 16
01106-038
where:
I
LOAD
is the AD859x output load current.
V
SY
is the AD859x supply voltage.
V
OUT
is the output voltage.
SNUBBER
IN CIRCUIT
AD [ ANALOG DEVICES ]
