LMV716MMX datasheet(9/15 Pages) NSC

9 / 15 page

Application Information

With the low supply current of only 1.6 mA, the LMV716

offers users the ability to maximize battery life. This makes

the LMV716 ideal for battery powered systems. The

LMV716’s rail-to-rail output swing provides the maximum

possible dynamic range at the output. This is particularly

important when operating on low supply voltages.

CAPACITIVE LOAD TOLERANCE

The LMV716, when in a unity-gain configuration, can directly

drive large capacitive loads in unity-gain without oscillation.

The unity-gain follower is the most sensitive configuration to

capacitive loading; direct capacitive loading reduces the

phase margin of amplifiers. The combination of the amplifi-

er’s output impedance and the capacitive load induces

phase lag. This results in either an underdamped pulse

response or oscillation. To drive a heavier capacitive load,

the circuit in Figure 1 can be used.

In Figure 1, the isolation resistor R

ISO and the load capacitor

L form a pole to increase stability by adding more phase

margin to the overall system. The desired performance de-

pends on the value of R

ISO. The bigger the RISO resistor

value, the more stable V

OUT will be.

The circuit in Figure 2 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

ISO and the load resistor. Instead, in

Figure 2,R

provides the DC accuracy by using feed-

forward techniques to connect V

IN to RL. Due to the input

bias current of the LMV716, the designer must be cautious

when choosing the value of R

F.CF and RISO serve to coun-

teract the loss of phase margin by feeding the high fre-

quency component of the output signal back to the amplifi-

er’s inverting input, thereby preserving phase margin in the

overall feedback loop. Increased capacitive drive is possible

by increasing the value of C

F. This in turn will slow down the

pulse response.

DIFFERENCE AMPLIFIER

The difference amplifier allows the subtraction of two volt-

ages or, as a special case, the cancellation of a signal

common to two inputs. It is useful as a computational ampli-

fier in making a differential to single-ended conversion or in

rejecting a common mode signal.

20179507

FIGURE 1. Indirectly Driving a Capacitive Load using

Resistive Isolation

20179509

FIGURE 2. Indirectly Driving a Capacitive Load with DC

Accuracy

20179510

FIGURE 3. Difference Amplifier

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