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參數資料
| 型號： | AD8392ACP-R2 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 運動控制電子 |
| 英文描述： | Low Power, High Output Current, Quad Op Amp, Dual-Channel ADSL/ADSL2+ Line Driver |
| 中文描述： | QUAD OP-AMP, 5000 uV OFFSET-MAX, QCC32 |
| 封裝： | 5 X 5 MM, MO-220VHHD, LFCSP-32 |
| 文件頁數： | 13/16頁 |
| 文件大小： | 529K |
| 代理商： | AD8392ACP-R2 |
AD8392
THERMAL CONSIDERATIONS
When using a quad, high output current amplifier, such as the
AD8392, special consideration should be given to system level
thermal design. In applications such as ADSL/ADSL2+, the
AD8392 could be required to dissipate as much as 1.4 W or
more on chip. Under these conditions, particular attention
should be paid to the thermal design in order to maintain safe
operating temperatures on the die. To aid in the thermal design,
the thermal information in the Thermal Resistance section can
be combined with what follows here.
Rev. 0 | Page 13 of 16
The information in Table 4 and Figure 3 is based on a standard
JEDEC 4-layer board and a maximum die temperature of
150°C. To provide additional guidance and design suggestions, a
thermal study was performed under a set of conditions more
closely aligned with an actual ADSL/ADSL2+ application.
In a typical ADSL/ADSL2+ line card, component density usu-
ally dictates that most of the copper plane used for thermal
dissipation be internal. Additionally, each ADSL/ADSL2+ port
may be allotted only 1 square inch, or even less, of board space.
For these reasons, a special thermal test board was constructed
for this study. The 4-layer board measured approximately
4 inches × 4 inches and contained two internal 1 oz copper
ground planes, each measuring 2 inches × 3 inches. The top
layer contained signal traces and an exposed copper strip
inch × 3 inches to accommodate heat sinking, with no other
copper on the top or bottom of the board.
Three 28-lead TSSOPs were placed on the board representing
six ADSL channels, or one channel per square inch of copper,
with each channel dissipating 700 mW on-chip (1.4 W per
package). The die temperature is then measured in still air and
in a wind tunnel with calibrated airflow of 100 LFM, 200 LFM,
and 400 LFM. Figure 36 shows the power dissipation versus the
ambient temperature for each airflow condition. The figure
assumes a maximum die temperature of 135°C. No heat sink
was used.
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5
15
25
35
45
55
65
75
85
AMBIENT TEMPERATURE (
°
C)
P
T
J
= 135
°
C
0
STILL AIR
100LFM
200LFM
400LFM
Figure 36. Power Dissipation vs. Ambient
Temperature and Air Flow 28-Lead TSSOP/EP
This data is only provided as guidance to assist in the thermal
design process. Due diligence should be performed with regards
to power dissipation because there are many factors that can
affect thermal performance.
TYPICAL ADSL/ADSL2+ APPLICATION
In a typical ADSL/ADSL2+ application, a differential line driver
is used to take the signal from the analog front end (AFE) and
drive it onto the twisted pair telephone line. Referring to the
typical circuit representation in Figure 37, the differential input
appears at V
IN+
and V
IN
from the AFE, while the differential
output is transformer coupled to the telephone line at tip and
ring. The common-mode operating point, generally midway
between the supplies, is set through V
COM
.
0
R4
R4
R3
R3
R
m
R2
R1
R2
V
COM
1:N
TIP
RING
R
OUT
R
IN
R
m
V
OA
V
OA
V
P
V
P
R
BIAS
R
BIAS
V
IN–
V
IN+
Figure 37. Typical ADSL/ADSL2+ Application Circuit
In ADSL/ADSL2+ applications, it is common practice to
conserve power by using positive feedback to synthesize the
output resistance, thereby lowering the required ohmic value of
the line matching resistors, R
m
. The circuit in Figure 37 is
somewhat unique in that the positive feedback introduced via
R3 has the effect of synthesizing the input resistance as well.
The following definitions and equations can be used to calculate
the resistor values necessary to obtain the desired gain, input
resistance, and output resistance for a given application. For
simplicity the following calculations assume a lossless
transformer.
The following values are used in the design equations and are
assumed already known or chosen by the designer.
V
IN
R
IN
N
V
LINE
R
m
Differential input voltage
Desired differential input resistance
Transformer turns ratio
Differential output voltage at tip and ring
Each is typically 5% to 15% of the transformer reflected
line impedance
Recommended in the amplifier data sheet
Voltage at the + inputs to the amplifier, approximately
V
IN
(must be less than V
IN
for positive input resistance)
Transformer reflected line impedance
R2
V
P
R
L
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