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

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

FREQUENCY (MHz)

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

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.