Datasheet

LMV710-N, LMV711-N, LMV715-N
SNOS519J –APRIL 2000–REVISED MARCH 2013 www.ti.com
(2)
The paralleled R
F
and C
F
introduce a zero, which cancels the effect from the pole.
Capacitive Load Tolerance
The LMV710-N/LMV711/ LMV715 can directly drive 200 pF 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 amplifier'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,
circuit in Figure 40 can be used.
Figure 40. Indirectly Driving A Capacitive Load using Resistive Isolation
In Figure 40, 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 depends on the value of R
ISO
. The bigger the R
ISO
resistor value, the more stable V
OUT
will be. But the DC accuracy is not great when the R
ISO
gets bigger. If there
were a load resistor in Figure 40, the output would be voltage divided by R
ISO
and the load resistor.
The circuit in Figure 41 is an improvement to the one in Figure 40 because it provides DC accuracy as well as
AC stability. In this circuit, R
F
provides the DC accuracy by using feed-forward techniques to connect V
IN
to R
L
.
C
F
and R
ISO
serve to counteract the loss of phase margin by feeding the high frequency component of the output
signal back to the amplifier'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.
Figure 41. Indirectly Driving A Capacitive A Load with DC Accuracy
Application Circuits
Peak Detector
Peak detectors are used in many applications, such as test equipment, measurement instrumentation, ultrasonic
alarm systems, etc. Figure 42 shows the schematic diagram of a peak detector using LMV710-N or LMV711 or
LMV715. This peak detector basically consists of a clipper, a parallel RC network, and a voltage follower.
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