Application Information

BENEFITS OF THE LPV321/358/324

Size

The small footprints of the LPV321/358/324 packages save

space on printed circuit boards, and enable the design of

smaller electronic products, such as cellular phones, pagers,

or other portable systems. The low profile of the LPV321/

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 LPV321/358/324 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

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.

CAPACITIVE LOAD TOLERANCE

The LPV321/358/324 can directly drive 200 pF 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 1 can be used.

In Figure 1, the isolation resistor R

C

margin to the overall system. The desired performance de-

pends on the value of R

value, the more stable V

waveform of Figure 1 using 100 k

Ω for R

C

The circuit in Figure 3 is an improvement to the one in Figure

1 because it provides DC accuracy as well as AC stability. If

there were a load resistor in Figure 1, the output would be

voltage divided by R

Figure 3,R

F

provides the DC accuracy by using feed-

forward techniques to connect V

in choosing the value of R

the LPV321/358/324. C

loss of phase margin by feeding the high frequency compo-

nent of the output signal back to the amplifier’s inverting

input, thereby preserving phase margin in the overall feed-

back loop. Increased capacitive drive is possible by increas-

ing the value of C

response.

10092004

FIGURE 1. Indirectly Driving A Capacitive Load Using

Resistive Isolation

10092075

FIGURE 2. Pulse Response of the LPV324 Circuit in

Figure 1

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