Ω,R

Ω, unless otherwise

specified. (Continued)

Crosstalk (LMH6725)

20078945

Application Section

GENERAL INFORMATION

The LMH6723/LMH6724/LMH6725 is a high speed current

feedback amplifier manufactured on National Semiconduc-

tor’s VIP10 (Vertically Integrated PNP) complimentary bipo-

lar process. LMH6723/LMH6724/LMH6725 offers a unique

combination of high speed and low quiescent supply current

making it suitable for a wide range of battery powered and

portable applications that require high performance. This

amplifier can operate from 4.5V to 12V nominal supply volt-

ages and draws only 1 mA of quiescent supply current at

LMH6725 has no internal ground reference so single or split

supply configurations are both equally useful.

EVALUATION BOARDS

National Semiconductor provides the following evaluation

boards as a guide for high frequency layout and as an aid in

device testing and characterization. Many of the datasheet

plots were measured with these boards.

Device

Package

Board Part #

LMH6723MA

SOIC-8

CLC730227

LMH6723MF

SOT-23

CLC730216

LMH6724MA

SOIC-8

CLC730036

LMH6725MA

SOIC-14

CLC730231

These evaluation boards can be shipped when a device

sample request is placed with National Semiconductor.

FEEDBACK RESISTOR SELECTION

One of the key benefits of a current feedback operational

amplifier is the ability to maintain optimum frequency re-

sponse independent of gain by using appropriate values for

the feedback resistor (R

Typical Performance plots were generated with an R

1200

(unless otherwise specified). Generally, lowering R

recommended value will peak the frequency response and

extend the bandwidth; however, increasing the value of R

F

will cause the frequency response to roll off faster. Reducing

the value of R

cause overshoot, ringing and, eventually, oscillation.

Figure 1 shows the LMH6723/LMH6724/LMH6725’s fre-

quency response as R

Ω,A

plot shows that an R

Ω results in peaking. An R

1200

Ω gives near maximal bandwidth and gain flatness with

good stability. Since each application is slightly different it is

worth some experimentation to find the optimal R

given circuit. In general a value of R

~0.1 dB

of peaking is the best compromise between stability and

maximal bandwidth. Note that it is not possible to use a

current feedback amplifier with the output shorted directly to

the inverting input. The buffer configuration of the LMH6723/

LMH6724/LMH6725 requires a 2000

Ω feedback resistor for

stable operation. For other gains see the charts "R

20078922

FIGURE 1. Frequency Response vs. R

F

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