LMV791MK/NOPB National Semiconductor, LMV791MK/NOPB Datasheet - Page 14

• Manufacturer Part Number: LMV791MK/NOPB
• Description: IC OP AMP CMOS 1.8V TSOT23-6
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LMV791MK/NOPB

• Amplifier Type: General Purpose
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 11.5 V/µs
• Gain Bandwidth Product: 17MHz
• Current - Input Bias: 0.1pA
• Voltage - Input Offset: 100µV
• Current - Supply: 1.15mA
• Current - Output / Channel: 60mA
• Voltage - Supply, Single/dual (±): 1.8 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-6, TSOT-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Other names: LMV791MK; LMV791MKNOPB; LMV791MKNOPBTR; LMV791MKNOPBTR; LMV791MKTR

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Application Information
ADVANTAGES OF THE LMV791/LMV792
Wide Bandwidth at Low Supply Current
The LMV791 and LMV792 are high performance op amps that
provide a unity gain bandwidth of 17 MHz while drawing a low
supply current of 1.15 mA. This makes them ideal for provid-
ing wideband amplification in portable applications. The en-
able and shutdown feature can also be used to design more
power efficient systems that offer wide bandwidth and high
performance while consuming less average power.
Low Input Referred Noise and Low Input Bias Current
The LMV791/LMV792 have a very low input referred voltage
noise density (5.8 nV/
sures a small input bias current (100 fA) and low input referred
current noise (0.01 pA/
ing signal fidelity, and makes the LMV791 and LMV792 ideal
for audio and sensor based applications.
Low Supply Voltage
The LMV791 and the LMV792 have performance guaranteed
at 2.5V and 5V supply. The LMV791 family is guaranteed to
be operational at all supply voltages between 2.0V and 5.5V,
for ambient temperatures ranging from −40°C to 125°C, thus
utilizing the entire battery lifetime. The LMV791 and LMV792
are also guaranteed to be operational at 1.8V supply voltage,
for temperatures between 0°C and 125°C. This makes the
LMV791 family ideal for usage in low-voltage commercial ap-
plications.
RRO and Ground Sensing
Rail-to-rail output swing provides maximum possible dynamic
range at the output. This is particularly important when oper-
ating at low supply voltages. An innovative positive feedback
scheme is used to boost the current drive capability of the
output stage. This allows the LMV791 and the LMV792 to
source more than 40 mA of current at 1.8V supply. This also
limits the performance of the LMV791 family as comparators,
and hence the usage of the LMV791 and the LMV792 in an
open-loop configuration is not recommended. The input com-
mon-mode range includes the negative supply rail which
allows direct sensing at ground in single supply operation.
Enable and Shutdown Features
The LMV791 family is ideal for battery powered systems. With
a low supply current of 1.15 mA and a shutdown current of
140 nA typically, the LMV791 and LMV792 allow the designer
to maximize battery life. The enable pin of the LMV791 and
the LMV792 allows the op amp to be turned off and reduce
its supply current to less than 1 μA. To power on the op amp
the enable pin should be higher than V
the positive supply. To disable the op amp, the enable pin
voltage should be less than V
ative supply.
at 1 kHz). A CMOS input stage en-
). This is very helpful in maintain-
−
+ 0.5V, where V
+
- 0.5V, where V
−
is the neg-
+
is
14
Small Size
The small footprint of the LMV791 and the LMV792 package
saves space on printed circuit boards, and enables the design
of smaller electronic products, such as cellular phones,
pagers, or other portable systems. Long traces between the
signal source and the opamp make the signal path suscepti-
ble to noise. By using a physically smaller LMV791 and
LMV792 package, the opamp can be placed closer to the sig-
nal source, reducing noise pickup and increasing signal in-
tegrity.
CAPACITIVE LOAD TOLERANCE
The LMV791 and LMV792 can directly drive 120 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 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, the 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
the more stable V
result in a reduced output swing and short circuit current.
INPUT CAPACITANCE AND FEEDBACK CIRCUIT
ELEMENTS
The LMV791 family has a very low input bias current (100 fA)
and a low 1/f noise corner frequency (400 Hz), which makes
it ideal for sensor applications. However, to obtain this per-
formance a large CMOS input stage is used, which adds to
the input capacitance of the op-amp, C
not affect the DC and low frequency performance, at higher
frequencies the input capacitance interacts with the input and
the feedback impedances to create a pole, which results in
lower phase margin and gain peaking. This can be controlled
by being selective in the use of feedback resistors, as well as
by using a feedback capacitance, C
verting amplifier shown in Figure 2, if C
and the open loop gain of the op amp is considered infinite
then the gain of the circuit is −R
usually has a dominant pole, which causes its gain to drop
with frequency. Hence, this gain is only valid for DC and low
frequency. To understand the effect of the input capacitance
coupled with the non-ideal gain of the op amp, the circuit
needs to be analyzed in the frequency domain using a
Laplace transform.
L
form a pole to increase stability by adding more phase
FIGURE 1. Isolation of C
OUT
will be. Increased R
ISO
. The bigger the R
L
2
to Improve Stability
/R
ISO
F
1
. For example, in the in-
. An op amp, however,
and the load capacitor
IN
IN
ISO
. Though this does
and C
ISO
would, however,
20116861
resistor value,
F
are ignored