LM6142BIN National Semiconductor, LM6142BIN Datasheet - Page 12

• Manufacturer Part Number: LM6142BIN
• Description: IC, OP-AMP, 17MHZ, 25V/µS, DIP-8
• Manufacturer: National Semiconductor

Specifications of LM6142BIN

• Op Amp Type: General Purpose
• No. Of Amplifiers: 2
• Bandwidth: 17MHz
• Slew Rate: 25V/µs
• Supply Voltage Range: 1.8V To 24V
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +85°C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Typical Applications
ANALOG TO DIGITAL CONVERTER BUFFER
The high capacitive load driving ability, rail-to-rail input and
output range with the excellent CMR of 82 dB, make the
LM6142/44 a good choice for buffering the inputs of A to D
converters.
3 OPAMP INSTRUMENTATION AMP WITH
RAIL-TO-RAIL INPUT AND OUTPUT
Using the LM6144, a 3 opamp instrumentation amplifier with
rail-to-rail inputs and rail to rail output can be made. These
features make these instrumentation amplifiers ideal for
single supply systems.
Some manufacturers use a precision voltage divider array of
5 resistors to divide the common-mode voltage to get an in-
put range of rail-to-rail or greater. The problem with this
method is that it also divides the signal, so to even get unity
gain, the amplifier must be run at high closed loop gains.
This raises the noise and drift by the internal gain factor and
lowers the input impedance. Any mismatch in these preci-
sion resistors reduces the CMR as well. Using the LM6144,
all of these problems are eliminated.
In this example, amplifiers A and B act as buffers to the dif-
ferential stage ( Figure 6 ). These buffers assure that the input
impedance is over 100 M
ment for precision matched resistors in the input stage. They
also assure that the difference amp is driven from a voltage
source. This is necessary to maintain the CMR set by the
matching of R1–R2 with R3–R4.
and they eliminate the require-
(Continued)
12
The gain is set by the ratio of R2/R1 and R3 should equal R1
and R4 equal R2. Making R4 slightly smaller than R2 and
adding a trim pot equal to twice the difference between R2
and R4 will allow the CMR to be adjusted for optimum.
With both rail to rail input and output ranges, the inputs and
outputs are only limited by the supply voltages. Remember
that even with rail-to-rail output, the output can not swing
past the supplies so the combined common mode voltage
plus the signal should not be greater than the supplies or lim-
iting will occur.
SPICE MACROMODEL
A SPICE macromodel of this and many other National Semi-
conductor opamps is available at no charge from the NSC
Customer Response Group at 800-272-9959.
FIGURE 6.
DS012057-13