DescriptionIC AMP XDSL LINE DVR 28-TSSOP
ManufacturerAnalog Devices Inc
TypeDriver

ProtocolxDSLVoltage - Supply3 V ~ 13 V
Mounting TypeSurface MountPackage / Case28-TSSOP Exposed Pad, 28-eTSSOP, 28-HTSSOP
Power Supply RequirementDualPackage TypeTSSOP EP
Slew Rate1000V/usPin Count28
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Page 14/20
PrevNext
one can use symmetry to simplify the computation for a dc
input signal.
=
×
×
+
×
P
2
I
V
4
D
Q
S
where:
V
is the peak output voltage of an amplifier.
O
This formula is slightly pessimistic due to the fact that some of
the quiescent supply current is commutated during sourcing or
sinking current into the load. For a sine wave source, integration
over a half cycle yields
4
=
×
×
+
P
2
I
V
2
D
Q
S
The situation is more complicated with a complex modulated
signal. In the case of a DMT signal, taking the equivalent sine
wave power overestimates the power dissipation by ~23%. For
example:
P
= 23.4 dBm = 220 mW
OUT
@ 50 Ω = 3.31 V rms
V
OUT
V
= 2.354 V
O
at each amplifier output, which yields a P
Through measurement, a DMT signal of 23.4 dBm requires
1.47 W of power to be dissipated by the AD8016. Figure 41
shows the results of calculation and actual measurements
detailing the relationship between the power dissipated by the
AD8016 versus the total output power delivered to the back
termination resistors and the load combined. A 1:2 transformer
turns ratio was used in the calculations and measurements.
2.5
2.0
CALCULATED
1.5
MEASURED
1.0
DMT
0.5
0
0
100
OUTPUT POWER (mW)
Figure 41. Power Dissipation vs. Output Power (Including
Back Terminations), See Figure 7 for Test Circuit
THERMAL ENHANCEMENTS AND PCB LAYOUT
There are several ways to enhance the thermal capacity of the
CO solution. Additional thermal capacity can be created using
enhanced PCB layout techniques such as interlacing (sometimes
referred to as stitching or interconnection) of the layers immedi-
ately beneath the line driver. This technique serves to increase
the thermal mass or capacity of the PCB immediately beneath
the driver. (See AD8016-EVAL boards for an example of this
method of thermal enhancement.) A cooling fan that draws
moving air over the PCB and xDSL drivers, while not always
required, may be useful in reducing the operating temperature
of the die, allowing more drive within the CO design. The
AD8016, whether in a PSOP3 (ARP) or SO-Batwing (ARB)
package, can be designed to operate in the CO solution using
V
O
(
V
V
)
prudent measures to manage the power dissipation through careful
S
O
R
PCB design. The PSOP3 package is available for use in design-
L
ing the highest density CO solutions. Maximum heat transfer to
the PCB can be accomplished using the PSOP3 package when
the thermal slug is soldered to an exposed copper pad directly
beneath the AD8016. Optimum thermal performance can be
achieved in the ARE package only when the back of the package
is soldered to a PCB designed for maximum thermal capacity
(see Figure 44). Thermal experiments with the PS0P3 package
were conducted without soldering the heat slug to the PCB.
2
V V
V
O
S
O
Heat transfer was through physical contact only. The following
π
R
R
offers some insight into the AD8016 power dissipation and
L
L
relative junction temperature, as well as the effects of PCB size
and composition on the junction-to-air thermal resistance or θ
THERMAL TESTING
A wind tunnel study was conducted to determine the relationship
between thermal capacity (i.e., printed circuit board copper area),
air flow, and junction temperature. Junction-to-ambient ther-
mal resistance, θ
of 1.81 W.
D
operated in a noninverting differential driver configuration, typical
of an xDSL application yet isolated from any other modem
components. Testing was conducted using a 1 oz. copper
board in an ambient temperature of ~24°C over air flows of
200, 150, 100, and 50 (0.200 and 400 for AD8016ARE) linear
feet per minute (LFM) and for ARP and ARB packages as well
as in still air. The 4-layer PCB was designed to maximize the
area of copper on the outer two layers of the board, while the
inner layers were used to configure the AD8016 in a differential
driver circuit. The PCB measured 3 inches × 4 inches in the
beginning of the study and was progressively reduced in size
to approximately 2 × 2 inches. The testing was performed in a
wind tunnel to control air flow in units of LFM. The tunnel is
approximately 11 inches in diameter.
MEASURED
AIR FLOW TEST CONDITIONS
SINE
DUT Power: Typical DSL DMT signal produces about 1.5 W
of power dissipation in the AD8016 package. The fully biased
(PWDN0 and PWDN1 = Logic 1) quiescent current of the
AD8016 is ~25 mA. A 1 MHz differential sine wave at an
amplitude of 8 V p-p/amplifier into an R
(50 Ω per side) produces the 1.5 W of power typical in the
AD8016 device. (See the Power Dissipation section for details.)
200
300
Thermal Resistance: The junction-to-case thermal resistance
) of the AD8016ARB or SO-Batwing package is 8.6°C/W, for
JC
the AD8016ARE or TSSOP-EP it is 5.6°C/W, and for the
AD8016ARP or PSOP3 package it is 0.86°C/W. These package
specifications were used in this study to determine junction
temperature based on the measured case temperature.
PCB Dimensions of a Differential Driver Circuit: Several
components are required to support the AD8016 in a differential
driver circuit. The PCB area necessary for these components (i.e.,
feedback and gain resistors, ac-coupling and decoupling capaci-
tors, termination and load resistors) dictated the area of the
smallest PCB in this study, 4.7 square inches. Further reduction
in PCB area, although possible, has consequences in terms of
the maximum operating junction temperature.
–14–
, was also calculated for the AD8016ARP,
JA
of 100 Ω differential