LM7341MFE datasheet(14/20 Pages) NSC

14 / 20 page

THD+N vs. Frequency

20206053

Application Information

GENERAL INFORMATION

Low supply current and wide bandwidth, greater than rail-to-

rail input range, full rail-to-rail output, good capacitive load

driving ability, wide supply voltage and low distortion all make

the LM7341 ideal for many diverse applications.

The high common-mode rejection ratio and full rail-to-rail in-

put range provides precision performance when operated in

non-inverting applications where the common-mode error is

added directly to the other system errors.

CAPACITIVE LOAD DRIVING

The LM7341 has the ability to drive large capacitive loads. For

example, 1000 pF only reduces the phase margin to about 30

degrees.

POWER DISSIPATION

Although the LM7341 has internal output current limiting,

shorting the output to ground when operating on a +30V pow-

er supply will cause the op amp to dissipate about 350 mW.

This is a worst-case example. In the 5-pin SOT-23 package,

the higher thermal resistance will cause a calculated rise of

113°C. This can raise the junction temperature to above the

absolute maximum temperature of 150°C.

Operating from split supplies greatly reduces the power dis-

sipated when the output is shorted. Operating on ±15V sup-

plies can only cause a temperature rise of 57°C in the 5-pin

SOT-23 package, assuming the short is to ground.

WIDE SUPPLY RANGE

The high power-supply rejection ratio (PSRR) and common

mode rejection ratio (CMRR) provide precision performance

when operated on battery or other unregulated supplies. This

advantage is further enhanced by the very wide supply range

(2.5V–32V) offered by the LM7341. In situations where highly

variable or unregulated supplies are present, the excellent

PSRR and wide supply range of the LM7341 benefit the sys-

tem designer with continued precision performance, even in

such adverse supply conditions.

SPECIFIC ADVANTAGES OF 5-Pin SOT-23 (TinyPak)

The obvious advantage of the 5-pin SOT-23, TinyPak, is that

it can save board space, a critical aspect of any portable or

miniaturized system design. The need to decrease overall

system size is inherent in any handheld, portable, or

lightweight system application.

Furthermore, the low profile can help in height limited designs,

such as consumer hand-held remote controls, sub-notebook

computers, and PCMCIA cards.

An additional advantage of the tiny package is that it allows

better system performance due to ease of package place-

ment. Because the tiny package is so small, it can fit on the

board right where the op amp needs to be placed for optimal

performance, unconstrained by the usual space limitations.

This optimal placement of the tiny package allows for many

system enhancements, not easily achieved with the con-

straints of a larger package. For example, problems such as

system noise due to undesired pickup of digital signals can

be easily reduced or mitigated. This pick-up problem is often

caused by long wires in the board layout going to or from an

op amp. By placing the tiny package closer to the signal

source and allowing the LM7341 output to drive the long wire,

the signal becomes less sensitive to such pick-up. An overall

reduction of system noise results.

Often times system designers try to save space by using dual

or quad op amps in their board layouts. This causes a com-

plicated board layout due to the requirement of routing several

signals to and from the same place on the board. Using the

tiny op amp eliminates this problem.

Additional space savings parts are available in tiny packages

from National Semiconductor, including low power amplifiers,

precision voltage references, and voltage regulators.

LOW DISTORTION, HIGH OUTPUT DRIVE CAPABILITY

The LM7341 offers superior low-distortion performance, with

a total-harmonic-distortion-plus-noise of −66 dB at f = 10 kHz.

The advantage offered by the LM7341 is its low distortion

levels, even at high output current and low load resistance.

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