LMP2012MMX National Semiconductor, LMP2012MMX Datasheet - Page 11

• Manufacturer Part Number: LMP2012MMX
• Description: IC,Operational Amplifier,DUAL,TSSOP,8PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LMP2012MMX

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Information
INPUT CURRENTS
The LMP201X’s input currents are different than standard
bipolar or CMOS input currents in that it appears as a current
flowing in one input and out the other. Under most operating
conditions, these currents are in the picoamp level and will
have little or no effect in most circuits. These currents tend to
increase slightly when the common-mode voltage is near the
minus supply. (See the typical curves.) At high temperatures
such as 85˚C, the input currents become larger, 0.5 nA
typical, and are both positive except when the V
V
and high temperature, do not add resistance in series with
the inputs to balance the impedances. Doing this can cause
an increase in offset voltage. A small resistance such as 1
kΩ can provide some protection against very large transients
or overloads, and will not increase the offset significantly.
−
. If operation is expected at low common-mode voltages
FIGURE 2.
FIGURE 3.
(Continued)
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CM
is near
11
PRECISION STRAIN-GAUGE AMPLIFIER
This Strain-Gauge amplifier (Figure 4) provides high gain
(1006 or ~ 60 dB) with very low offset and drift. Using the
resistors’ tolerances as shown, the worst case CMRR will be
greater than 108 dB. The CMRR is directly related to the
resistor mismatch. The rejection of common-mode error, at
the output, is independent of the differential gain, which is
set by R3. The CMRR is further improved, if the resistor ratio
matching is improved, by specifying tighter-tolerance resis-
tors, or by trimming.
Extending Supply Voltages and Output Swing by Using
a Composite Amplifier Configuration:
In cases where substantially higher output swing is required
with higher supply voltages, arrangements like the ones
shown in Figure 5 and Figure 6 could be used. These
configurations utilize the excellent DC performance of the
LMP201X while at the same time allow the superior voltage
and frequency capabilities of the LM6171 to set the dynamic
performance of the overall amplifier. For example, it is pos-
sible to achieve
GBW (A
due to V
kept at about mid-point of its overall supply voltage, and its
input common mode voltage range allows the V- terminal to
be grounded in one case (Figure 5, inverting operation) and
tied to a small non-critical negative bias in another (Figure 6,
non-inverting operation). Higher closed-loop gains are also
possible with a corresponding reduction in realizable band-
width. Table 1 shows some other closed loop gain possibili-
ties along with the measured performance in each case.
V
OS
= 100) while keeping the worst case output shift
less than 4 mV. The LMP201X output voltage is
±
12V output swing with 300 MHz of overall
FIGURE 4.
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