LMH6732MFX datasheet(14/19 Pages) NSC

14 / 19 page

Application Information:

DESCRIPTION

The LMH6732 is an adjustable supply current, current-

feedback operational amplifier. Supply current and conse-

quently dynamic performance can be easily adjusted by

selecting the value of a single external resistor (R

P).

Note: Note: The following discussion uses the SOIC package pin numbers.

For the corresponding SOT23-6 package pin numbers, please refer to

the Connection Diagram section.

SELECTING AN OPERATING POINT

The operating point is determined by the supply current

which in turn is determined by current (I

P) flowing out of pin

8. As the supply current is increased, the following effects

will be observed:

TABLE 1. Device Parameters Related to Supply

Current

Specification

Effect as I

CC Increases

Bandwidth

Increases

Rise Time

Decreases

Enable/ Disable Speed

Increases

Output Drive

Increases

Input Bias Current

Increases

Input Impedance

Decreases (see Source

impedance Discussion)

Both the Electrical Characteristics pages and the Typical

Performance Characteristics section illustrate these effects

to help make the supply current vs. performance trade-off.

The supply current is adjustable over a continuous range of

more than 10 to 1 with a single resistor, R

P, allowing for easy

trade-off between power consumption and speed. Perfor-

mance is specified and tested at I

CC = 1mA, 3.4mA, and

9mA. (Note: Some test conditions and especially the load

resistances are different for the three supply current set-

tlings.) The performance plots show typical performance for

all three supply currents levels.

When making the supply current vs. performance trade-off, it

is first a good idea to see if one of the standard operating

points (I

CC = 1mA, 3.4mA, or 9mA) fits the application. If it

does, performance guaranteed on the specification pages

will apply directly to your application. In addition, the value of

P may be obtained directly from the Electrical Characteris-

tics pages.

BEYOND 1GHz BANDWIDTH

As stated above, the LMH6732 speed can be increased by

increasing the supply current. The −3dB Bandwidth can

even reach the unprecedented value of 1.5GHz (A

V = +2,

OUT = 0.25VPP). Of course, this comes at the expense of

power consumption (i.e. supply current). The relationship

between −3dB BW and supply current is shown in the Typi-

cal Performance Characteristics section. The supply current

would nominally have to be set to around 10mA to achieve

this speed. The absolute maximum supply current setting for

the LMH6732 is 14mA. Beyond this value, the operation may

become unpredictable.

The following discussion will assist in selecting I

CC for

applications that cannot operate at one of the specified

supply current settlings.

Use the typical performance plots for critical specifications to

select the best I

CC. For parameters containing Min/Max rat-

ings in the data sheet tables, interpolate between the values

of I

CC in the plots & specification tables to estimate the

max/min values in the application.

The simplified schematic for the supply current setting path

P) is shown below in Figure 3.

20060258

FIGURE 1. Recommended Non-Inverting Gain Circuit

20060259

FIGURE 2. Recommended Inverting Gain Circuit

LMH6732MFX Datasheet(PDF) 14 Page - National Semiconductor (TI)

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