LM7131BCM5X National Semiconductor, LM7131BCM5X Datasheet - Page 19

• Manufacturer Part Number: LM7131BCM5X
• Description: Tiny High Speed Single Supply Operational Amplifier
• Manufacturer: National Semiconductor

Using the LM7131
The LM7131 can also supply +2.00V to a 50
ground, making it useful as driver in 50
portable test equipment.
Cable Driving with +3V Supplies
The LM7131 can drive 150 to 2.00V when supplied by a 3V
supply. This 3V performance means that the LM7131 is use-
Audio and High Frequency Signal Processing
The LM7131 is useful for high fidelity audio and signal pro-
cessing. A typical LM7131 is capable of driving 2V across
150
4 MHz when powered by a single 5V supply.
Use with 2.5V Virtual Ground Systems
with +5V Single Supply Power
Many analog systems which must work on a single +5V sup-
ply use a “virtual ground” - a reference voltage for the signal
processing which is usually between +5V and 0V. This virtual
ground is usually halfway between the top and bottom sup-
ply rails. This is usually +2.5V for +5V systems and +1.5V for
+3V systems.
The LM7131 can be used in single supply/virtual ground sys-
tems driving loads referenced to 2.5V. The output swing
specifications in the data sheet show the tested voltage lim-
its for driving a 150
and +5V. A look at the output swing specifications shows that
for heavy loads like 150 ohms, the output will swing as close
as one diode drop (roughly, 0.7V) to the supply rail. This
leaves a relatively wide range for +5V systems and a some-
what narrow range for +3V systems. One way to increase
this output range is to have the output load referenced to
ground — this will allow the output to swing lower. Another is
to use higher load impedances. The output swing specifica-
tions show typical numbers for swing with loads of 600
(referenced to ground) at less than 0.1% distortion at
load to a virtual ground supply for +3V
(Continued)
systems such as
FIGURE 14. CCD Amplifier
load to
to
19
ful in battery powered video applications, such as camcord-
ers, portable video mixers, still video cameras, and portable
scanners.
ground. Note that these typical numbers are similar to those
for a 150
the maximum DC performance of the LM7131.
The sinking output of the LM7131 is somewhat lower than
the amplifier’s sourcing capability. This means that the
LM7131 will not drive as much current into a load tied to 2.5
V as it will drive into a load tied to 0V.
Good AC performance will require keeping the output further
away from the supply rails. For a +5V supply and relatively
high impedance load (analog-to-digital converter input) the
following are suggested as an initial starting range for
achieving high (
Upper output level —
Approximately 0.8V to 1V below the positive (V+) rail.
Lower output level —
Approximately 200 mV–300 mV above the negative rail.
The LM7131 very useful in virtual ground systems as an out-
put device for output loads which are referenced to 0V or the
lower rail. It is also useful as a driver for capacitive loads,
such as sample and hold circuits, and audio analog to digital
converters. If fast amplifiers with rail-to-rail output ranges are
needed, please see the National Semiconductor LM6142
datasheet.
load. These typical numbers are an indication of
>
60 dB) AC accuracy
DS012313-23
www.national.com