LMP7732MM National Semiconductor, LMP7732MM Datasheet - Page 14

• Manufacturer Part Number: LMP7732MM
• Description: IC, OP AMP, PREC RRIO, DUAL, 8SOIC
• Manufacturer: National Semiconductor

Specifications of LMP7732MM

• Op Amp Type: Precision
• No. Of Amplifiers: 2
• Bandwidth: 22MHz
• Slew Rate: 2.4V/µs
• Supply Voltage Range: 1.8V To 5.5V
• Amplifier Case Style: MSOP
• No. Of Pins: 8
• Operating Temperature Range: -40°C To
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Application Notes
LMP7732
The LMP7732 is a dual low noise, low offset voltage, rail-to-
rail input and output, low voltage precision amplifier.
The low input voltage noise of only 2.9 nV/
ner at 3 Hz makes the LMP7732 ideal for sensor applications
where DC accuracy is of importance.
The LMP7732 has very low guaranteed offset voltage of only
±40 µV. This low offset voltage along with the very low input
voltage noise allows higher signal integrity and higher signal
to noise ratios since the error contribution by the amplifier is
at a minimum.
The LMP7732 has high gain bandwidth of 22 MHz. This wide
bandwidth enables the use of the amplifier at higher gain set-
tings while retaining ample usable bandwidth for the applica-
tion. This is particularly beneficial when system designers
need to use sensors with very limited output voltage range as
it allows larger gains in one stage which in turn increases sig-
nal to noise ratio.
The LMP7732 has a proprietary input bias cancellation cir-
cuitry on the input stages. This allows the LMP7732 to have
only about 1.5 nA bias current with a bipolar input stage. This
low input bias current, paired with the inherent lower input
voltage noise of bipolar input stages makes the LMP7732 an
excellent choice for precision applications. The combination
of low input bias current, low input offset voltage, and low input
voltage noise enables the user to achieve unprecedented ac-
curacy and higher signal integrity.
National Semiconductor is heavily committed to precision
amplifiers and the market segment they serve. Technical sup-
port and extensive characterization data is available for sen-
sitive applications or applications with a constrained error
budget.
The LMP7732 comes in the 8-Pin SOIC and MSOP pack-
ages. These small packages are ideal solutions for area
constrained PC boards and portable electronics.
INPUT BIAS CURRENT CANCELLATION
The LMP7732 has proprietary input bias current cancellation
circuitry on its input stage.
The LMP7732 has rail-to-rail input. This is achieved by having
a p-input and n-input stage in parallel. Figure 1 only shows
FIGURE 2. 0.1 Hz to 10 Hz Noise Test Circuit
with a 1/f cor-
14
one of the input stages as the circuitry is symmetrical for both
stages.
Figure 1 shows that as the common mode voltage gets closer
to one of the extreme ends, current I
This increased current shows as an increase in voltage drop
across resistor R
voltage contributes to the offset voltage of the amplifier. When
common mode voltage is in the mid-range, the transistors are
operating in the linear region and I
voltage drop due to I
of magnitude smaller than the amplifier's input offset voltage.
As the common mode voltage gets closer to one of the rails,
the offset voltage generated due to I
comparable to the amplifiers offset voltage.
INPUT VOLTAGE NOISE MEASUREMENT
The LMP7732 has very low input voltage noise. The peak-to-
peak input voltage noise of the LMP7732 can be measured
using the test circuit shown in Figure 2
FIGURE 1. Input Bias Current Cancellation
1
equal to I
1
across R
1
*R
1
1
can be ignored as it is orders
on IN+ of the amplifier. This
1
30015079
1
is significantly small. The
1
increases and becomes
significantly increases.
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