4

Application Information

Relevant Application Notes

The following Application Notes pertain to the HFA1150:

• AN9787 - An Intuitive Approach to Understanding

Current Feedback Amplifiers

• AN9420 - Current Feedback Amplifier Theory and

Applications

• AN9663-Converting from Voltage Feedback to Current

Feedback Amplifiers

• AN9891-Operating the HFA1150 from 5V Single

Supply

These publications may be obtained from Intersil’s web site

(http://www.intersil.com).

Performance Differences Between Packages

The HFA1150 is a high frequency current feedback

amplifier. As such, it is sensitive to parasitic capacitances

which influence the amplifier’s operation. The different

parasitic capacitances of the SOIC and SOT-23 packages

yield performance differences (notably bandwidth and

bandwidth related parameters) between the two devices -

see Electrical Specification tables for details.

Because of these performance differences, designers

should evaluate and breadboard with the same package

style to be used in production.

Note that some “Typical Performance Curves” have

separate graphs for each package type. Graphs not labeled

with a specific package type are applicable to both

packages.

Optimum Feedback Resistor

The enclosed frequency response graphs detail the

performance of the HFA1150 in various gains. Although the

voltage feedback amplifier, there is an appreciable decrease

in bandwidth at higher gains. This decrease can be

minimized by taking advantage of the current feedback

All current feedback amplifiers require a feedback resistor,

with the internal compensation capacitor, sets the dominant

pole of the frequency response. Thus, the amplifier’s

excessive peaking and overshoot (Note: Capacitive

feedback causes the same problems due to the feedback

impedance decrease at higher frequencies). At higher gains

trade-off of stability for bandwidth. The table below lists

expected bandwidth.

5V Single Supply Operation

This amplifier operates at single supply voltages down to

4.5V. The dramatic supply current reduction at this operating

condition (refer also to Figure 25) makes this op amp an

even better choice for low power 5V systems. Refer to

Application Note AN9891 for further information.

Driving Capacitive Loads

Capacitive loads, such as an A/D input, or an improperly

terminated transmission line will degrade the amplifier’s

phase margin resulting in frequency response peaking and

possible oscillations. In most cases, the oscillation can be

prior to the capacitance.

Figure 1 details starting points for the selection of this

combinations for the optimum bandwidth, stability, and

settling time, but experimental fine tuning is recommended.

Picking a point above or to the right of the curve yields an

overdamped response, while points below or left of the curve

indicate areas of underdamped performance.

limiting system bandwidth well below the amplifier bandwidth

the maximum bandwidth is obtained without sacrificing

stability. In spite of this, bandwidth still decreases as the load

OPTIMUM FEEDBACK RESISTOR

SOIC/SOT-23

BANDWIDTH (MHz)

SOIC/SOT-23

-1

422/464

650/540

+1

600/500

+2

576/499

700/540

+5

348/422

480/400

+10

178/348

380/300

HFA1150