LMV321 datasheet(13/27 Pages) NSC

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Application Notes

1.0 BENEFITS OF THE LMV321/358/324

Size: The small footprints of the LMV321/358/324 packages

save space on printed circuit boards, and enable the design

of smaller electronic products, such as cellular phones, pag-

ers, or other portable systems. The low profile of the

LMV321/358/324 make them possible to use in PCMCIA

type III cards.

Signal Integrity

Signals can pick up noise between the signal source and the

amplifier. By using a physically smaller amplifier package,

the LMV321/358/324 can be placed closer to the signal

source, reducing noise pickup and increasing signal integrity.

Simplified Board Layout

These products help you to avoid using long pc traces in

your pc board layout. This means that no additional compo-

nents, such as capacitors and resistors, are needed to filter

out the unwanted signals due to the interference between

the long pc traces.

Low Supply Current

These devices will help you to maximize battery life. They

are ideal for battery powered systems.

Low Supply Voltage

National provides guaranteed performance at 2.7V and 5V.

These guarantees ensure operation throughout the battery

lifetime.

Rail-to-Rail Output

Rail-to-rail output swing provides maximum possible dy-

namic range at the output. This is particularly important

when operating on low supply voltages.

Input Includes Ground

Allows direct sensing near GND in single supply operation.

The differential input voltage may be larger than V

+ without

damaging the device. Protection should be provided to pre-

vent the input voltages from going negative more than −0.3V

(at 25˚C). An input clamp diode with a resistor to the IC input

terminal can be used.

Ease Of Use & Crossover Distortion

The LMV321/358/324 offer specifications similar to the fa-

miliar LM324. In addition, the new LMV321/358/324 effec-

tively eliminate the output crossover distortion. The scope

photos in Figure 1 and Figure 2 compare the output swing of

the LMV324 and the LM324 in a voltage follower configura-

tion, with V

S= ± 2.5V and RL (= 2k

Ω) connected to GND. It

is apparent that the crossover distortion has been eliminated

in the new LMV324.

2.0 CAPACITIVE LOAD TOLERANCE

The LMV321/358/324 can directly drive 200pF in unity-gain

without oscillation. The unity-gain follower is the most sensi-

tive configuration to capacitive loading. Direct capacitive

loading reduces the phase margin of amplifiers. The combi-

nation of the amplifier’s output impedance and the capacitive

load induces phase lag. This results in either an under-

damped pulse response or oscillation. To drive a heavier

capacitive load, circuit in Figure 3 can be used.

Time (50

µs/div)

10006097

FIGURE 1. Output Swing of LMV324

Time (50

µs/div)

10006098

FIGURE 2. Output Swing of LM324

10006004

FIGURE 3. Indirectly Driving A Capacitive Load Using

Resistive Isolation

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