LMP7701MF/NOPB

Manufacturer Part NumberLMP7701MF/NOPB
DescriptionIC OP AMP PREC 12V RRIO SOT23-5
ManufacturerNational Semiconductor
SeriesLMP®
LMP7701MF/NOPB datasheet
 

Specifications of LMP7701MF/NOPB

Amplifier TypeGeneral PurposeNumber Of Circuits1
Output TypeRail-to-RailSlew Rate1.1 V/µs
Gain Bandwidth Product2.5MHzCurrent - Input Bias0.2pA
Voltage - Input Offset37µVCurrent - Supply790µA
Current - Output / Channel86mAVoltage - Supply, Single/dual (±)2.7 V ~ 12 V, ±1.35 V ~ 6 V
Operating Temperature-40°C ~ 125°CMounting TypeSurface Mount
Package / CaseSOT-23-5, SC-74A, SOT-25Number Of Channels1
Voltage Gain Db130 dBCommon Mode Rejection Ratio (min)88 dB
Input Voltage Range (max)12 VInput Voltage Range (min)2.7 V
Input Offset Voltage0.2 mV at 5 VOutput Current (typ)42 mA
Operating Supply Voltage3 V, 5 V, 9 VSupply Current1 mA at 5 V
Maximum Operating Temperature+ 125 CMounting StyleSMD/SMT
Minimum Operating Temperature- 40 CLead Free Status / RoHS StatusLead free / RoHS Compliant
-3db Bandwidth-Other namesLMP7701MF
LMP7701MFTR
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TOTAL NOISE CONTRIBUTION
The LMP7701/LMP7702/LMP7704 have very low input bias
current, very low input current noise, and very low input volt-
age noise. As a result, these amplifiers are ideal choices for
circuits with high impedance sensor applications.
Figure 8 shows the typical input noise of the LMP7701/
LMP7702/LMP7704 as a function of source resistance where:
e
denotes the input referred voltage noise
n
e
is the voltage drop across source resistance due to input
i
referred current noise or e
= R
* i
i
S
n
e
shows the thermal noise of the source resistance
t
e
shows the total noise on the input.
ni
Where:
The input current noise of the LMP7701/LMP7702/LMP7704
is so low that it will not become the dominant factor in the total
noise unless source resistance exceeds 300 MΩ, which is an
unrealistically high value.
As is evident in Figure 8, at lower R
dominated by the amplifier's input voltage noise. Once R
larger than a few kilo-Ohms, then the dominant noise factor
becomes the thermal noise of R
. As mentioned before, the
S
current noise will not be the dominant noise factor for any
practical application.
FIGURE 8. Total Input Noise
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HIGH IMPEDANCE SENSOR INTERFACE
Many sensors have high source impedances that may range
up to 10 MΩ. The output signal of sensors often needs to be
amplified or otherwise conditioned by means of an amplifier.
The input bias current of this amplifier can load the sensor's
output and cause a voltage drop across the source resistance
as shown in Figure 9, where V
The last term, I
prevent errors introduced to the system due to this voltage,
an op amp with very low input bias current must be used with
high impedance sensors. This is to keep the error contribution
by I
*R
BIAS
so that it will not become the dominant noise factor.
values, total noise is
S
is
S
pH electrodes are very high impedance sensors. As their
name indicates, they are used to measure the pH of a solu-
tion. They usually do this by generating an output voltage
which is proportional to the pH of the solution. pH electrodes
are calibrated so that they have zero output for a neutral so-
lution, pH = 7, and positive and negative voltages for acidic
or alkaline solutions. This means that the output of a pH elec-
trode is bipolar and has to be level shifted to be used in a
single supply system. The rate of change of this voltage is
usually shown in mV/pH and is different for different pH sen-
sors. Temperature is also an important factor in a pH elec-
trode reading. The output voltage of the senor will change with
temperature.
Figure 10 shows a typical output voltage spectrum of a pH
electrode. Note that the exact values of output voltage will be
different for different sensors. In this example, the pH elec-
trode has an output voltage of 59.15 mV/pH at 25°C.
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FIGURE 10. Output Voltage of a pH Electrode
The temperature dependence of a typical pH electrode is
shown in Figure 11. As is evident, the output voltage changes
with changes in temperature.
18
+
= V
– I
*R
IN
S
BIAS
S
*R
, shows the voltage drop across R
BIAS
S
less than the input voltage noise of the amplifier,
S
FIGURE 9. Noise Due to I
BIAS
. To
S
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