lmv924 National Semiconductor Corporation, lmv924 Datasheet - Page 16

• Manufacturer Part Number: lmv924
• Description: 1.8v, 1mhz, Low Power Operational Amplifiers With Rail-to-rail Input And Output
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Note
This V
and AC coupled signals if proper care is not taken. For large
input signals that include the V
namic range, this will cause distortion in the output signal.
One way to avoid such distortion is to keep the signal away
from the crossover. For example, in a unity gain buffer con-
figuration and with V
contain input-crossover distortion while a 3V peak-to-peak
signal centered at 1.5V will not contain input-crossover dis-
tortion as it avoids the crossover point. Another way to avoid
large signal distortion is to use a gain of −1 circuit which
avoids any voltage excursions at the input terminals of the
amplifier. In that circuit, the common mode DC voltage can
be set at a level away from the V
For small signals, this transition in V
dependent spurious signal in series with the input signal and
can effectively degrade small signal parameters such as
gain and common mode rejection ratio. To resolve this prob-
lem, the small signal should be placed such that it avoids the
V
In addition to the rail-to-rail performance, the output stage
can provide enough output current to drive 600
cause of the high current capability, care should be taken not
to exceed the 150˚C maximum junction temperature specifi-
cation.
5.0 Power-Supply Considerations
The LMV921/LMV922/LMV924 are ideally suited for use with
most battery-powered systems. The LMV921/LMV922/
LMV924 operate from a single +1.8V to +5.0V supply and
consumes about 145µA of supply current per Amplifier. A
Battery Type
OS
Ni - Cad
Alkaline
Lithium
crossover point.
NMH
OS
crossover point can create problems for both DC
Voltage (V)
Operating
S
1.5
2.7
1.2
1.2
= 5V, a 5V peak-to-peak signal will
TABLE 1. LMV921 Characteristics with Typical Battery Systems.
(Continued)
OS
crossover point in their dy-
OS
End-of-Life
Voltage (V)
OS
cross-over point.
0.9
2.0
0.9
1.0
shows up as a V
loads. Be-
Capacity AA
Size (mA -
1000
1000
375
500
h)
CM
16
high power supply rejection ratio of 78dB allows the amplifier
to be powered directly off a decaying battery voltage extend-
ing battery life.
Table 1 lists a variety of typical battery types. Batteries have
different voltage ratings; operating voltage is the battery volt-
age under nominal load. End-of-Life voltage is defined as the
voltage at which 100% of the usable power of the battery is
consumed. Table 1 also shows the typical operating time of
the LMV921.
6.0 Distortion
The two main contributors of distortion in LMV921/LMV922/
LMV924 family is:
1. Output crossover distortion occurs as the output transi-
tions from sourcing current to sinking current.
2. Input crossover distortion occurs as the input switches
from NPN to PNP transistor at the input stage.
To decrease crossover distortion:
1. Increase the load resistance. This lowers the output cross-
over distortion but has no effect on the input crossover dis-
tortion.
2. Operate from a single supply with the output always
sourcing current.
3. Limit the input voltage swing for large signals between
ground and one volt below the positive supply.
4. Operate in inverting configuration to eliminate common
mode induced distortion.
5. Avoid small input signal around the input crossover region.
The discontinuity in the offset voltage will effect the gain,
CMRR and PSRR.
time (Hours)
Operating
LMV921
6802
6802
2551
3401