ADA4312-1 Data Sheet
Rev. A | Page 10 of 12
Note that there is a trade-off between the adjusted quiescent
current and the linearity (or MTPR) of the transmitted signal.
Multitone power ratio (MTPR) was monitored at 5 MHz,
17 MHz, 28 MHz, 31 MHz, 59 MHz, and 82 MHz. Figure 18
can be used to gauge the approximate degradation of MTPR
vs. R
IADJ
and quiescent current while transmitting the G.hn
signal across a 40 Ω differential load in the circuit shown in
Figure 17.
–70
–65
–60
–55
–50
–45
–40
0 10 20 30 40 50 60 70 80 90
MTPR (dBc)
FREQUENCY (MHz)
8kΩ, I
Q
= 11mA
4kΩ, I
Q
= 18mA
1kΩ, I
Q
= 33mA
0Ω, I
Q
= 46.5mA
2kΩ, I
Q
= 26mA
11044-021
Figure 18. MTPR vs. R
IADJ
PCB LAYOUT
As is the case with many high speed line driver applications, care-
ful attention to printed circuit board (PCB) layout can improve
performance and help maintain stability while preventing excessive
die temperatures during normal operation. Differential signal
balance can be maintained by using symmetry in the PCB layout
of input and output signal traces.
Keeping the input and output traces as short as possible helps
prevent excessive parasitics from affecting overall performance
and stability. Keep the feedback resistors and gain setting resistor
as close to the line driver as physically possible. The back termi-
nation resistors and line coupling transformer should be placed
as close to the ADA4312-1 outputs as possible.
For more information about high speed board layout, see A
Practical Guide to High-Speed Printed-Circuit-Board Layout
(Analog Dialogue, Volume 39, September 2005).
THERMAL MANAGEMENT
The thermal pad of the ADA4312-1 is an electrically isolated
copper pad that should be soldered to an external thermal
ground plane. The number of thermal vias that connect the
exposed pad of the ADA4312-1 to the PCB can influence the
thermal conductivity of the PCB assembly. Moving heat away
from the ADA4312-1 die to the ambient environment is the
objective of a PCB designed in accordance with the guidelines
found in the AN-772 Application Note.
The outer layers of the PCB are the best choice to radiate heat
into the environment by convection. Conducting heat away
from the ADA4312-1 die into the outer layers of the PCB can
be accomplished with nine thermal vias connecting the exposed
pad to both outer layers. The vias can be spaced 0.75 mm apart
in a 3 × 3 matrix.
The ADA4312-1 evaluation board (EVAL-ADA4312-1ACPZ)
represents a robust example of an effective thermal management
approach (see Figure 19 and Figure 20).
For more information about thermal management, solder
assembly techniques for LFCSP packages, and important
package mechanical and materials information, refer to the
following link:
http://www.analog.com/en/technical-library/packages/csp-
chip-scale-package/lfcsp/index.html
POWER SUPPLY BYPASSING
The ADA4312-1 should be operated on a well-regulated single
+12 V power supply. Pay careful attention to power supply
decoupling. Use high quality capacitors with low equivalent series
resistance (ESR), such as multilayer ceramic capacitors (MLCCs),
to minimize supply voltage ripple and power dissipation.
Locate the 0.1 µF MLCC decoupling capacitor no more than
one-eighth of an inch away from the V
CC
supply pin. In addition,
a 10 µF tantalum capacitor is recommended to provide good
decoupling for lower frequency signals and to supply current for
fast, large signal changes at the ADA4312-1 outputs. Lay out
bypassing capacitors to keep return currents away from the
inputs of the amplifiers. A large ground plane provides a low
impedance path for the return currents.
