ADA4311-1

Rev. 0 | Page 11 of 16

APPLICATION INFORMATION

FEEDBACK RESISTOR SELECTION

The feedback resistor has a direct impact on the closed-loop

bandwidth and stability of the current feedback op amp.

Reducing the resistance below the recommended value can

make the amplifier response peak and even become unstable.

Increasing the size of the feedback resistor beyond the recom-

mended value reduces the closed-loop bandwidth. Table 5

provides a convenient reference for quickly determining the

feedback and gain resistor values, and the corresponding

bandwidth, for common gain configurations. The recommended

feedback resistor value for the ADA4311-1 is 499 Ω.

Table 5. Recommended Values and Frequency Performance1

Gain

−3 dB SS BW (MHz)

+5

499

124

310

+5

1 k

250

220

+10

499

55.4

175

+20

499

26.1

84

POWER CONTROL MODES OF OPERATION

The ADA4311-1 features four power modes: full power, ¾

power, ½ power, and shutdown. The power modes are controlled

by two logic pins, PD0 and PD1. The power-down control pins

are compatible with standard 3 V and 5 V CMOS logic. Table 6

shows the various power modes and associated logic states. In

the power-down mode, the output of the amplifier goes into a

high impedance state.

Table 6. Power Modes

PD1

PD0

Power Mode

Total Supply

Current (mA)

Output

Impedance

Low

Low

Full Power

23.6

Low

Low

High

¾ Power

15.8

Low

High

Low

½ Power

10.4

Low

High

High

Power-Down

1.8

High

EXPOSED THERMAL PAD CONNECTIONS

The exposed thermal pad on the 10-lead MSOP is both the

reference for the PD pins and the only electrical connection for

the negative supply voltage. Therefore, in the 10-lead MSOP,

the ADA4311-1 can only be used on a single supply. The exposed

thermal pad must be connected to ground. Failure to do so

renders the part inoperable.

A requirement for this package is that the thermal pad be

connected to a solid plane with low thermal resistance, ensuring

adequate heat transfer away from the die and into the board.

POWERLINE APPLICATION

Applications (that is, powerline AV modems) requiring greater

than 10 dBm peak power should consider using an external

line driver, such as the ADA4311-1. Figure 22 shows an example

interface between the TxDAC® output and the ADA4311-1 biased

for single-supply operation. The peak-to-peak differential

output voltage swing of the TxDAC should be limited to

2 V p-p, with the gain of the ADA4311-1 configured to realize

the additional voltage gain required by the application. A low-

pass filter should be considered to filter the DAC images

inherent in the signal reconstruction process. In addition, dc

blocking capacitors are required to level-shift the output signal

of the TxDAC to the common-mode level of the ADA4311-1

0.1µF

IOUTP+

IOUTP–

0dB TO –7.5dB

OPTIONAL

LCLPF

ADA4311-1

ADA4311-1

1/2

1/2

TxDAC

Figure 22. TxDAC Output Directly via Center-Tap Transformer