Datasheet

LMV791, LMV792
SNOSAG6F –SEPTEMBER 2005–REVISED MARCH 2013 www.ti.com
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 providing wideband amplification in portable
applications. The enable 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/√Hz at 1 kHz). A CMOS input
stage ensures a small input bias current (100 fA) and low input referred current noise (0.01 pA/√Hz). This is very
helpful in maintaining 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 ensured at 2.5V and 5V supply. The LMV791 family is ensured
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 ensured 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 applications.
RRO and Ground Sensing
Rail-to-rail output swing provides maximum possible dynamic range at the output. This is particularly important
when operating 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 common-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
+
- 0.5V, where V
+
is the positive supply. To
disable the op amp, the enable pin voltage should be less than V
−
+ 0.5V, where V
−
is the negative supply.
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 susceptible to noise. By using a physically
smaller LMV791 and LMV792 package, the opamp can be placed closer to the signal source, reducing noise
pickup and increasing signal integrity.
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 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, the circuit in
Figure 50 can be used.
In Figure 50, 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. Increased R
ISO
would, however, result in a reduced output swing and
short circuit current.
14 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated
Product Folder Links: LMV791 LMV792