LMV716 Datasheet, PDF (9/15 Pages) National Semiconductor (TI) – 5 MHz, Low Noise, RRO, Dual Operational Amplifier with CMOS Input

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.
20179509
FIGURE 2. Indirectly Driving a Capacitive Load with DC
Accuracy
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
In Figure 1, the isolation resistor R_ISO and the load capacitor
C_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 R_ISO 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_F provides the DC accuracy by using feed-
forward techniques to connect V_IN to R_L. Due to the input
bias current of the LMV716, the designer must be cautious
when choosing the value of R_F. C_F and R_ISO 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.
20179510
FIGURE 3. Difference Amplifier
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