LMP7701MF/NOPB National Semiconductor, LMP7701MF/NOPB Datasheet - Page 18

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LMP7701MF/NOPB

Manufacturer Part Number
LMP7701MF/NOPB
Description
IC OP AMP PREC 12V RRIO SOT23-5
Manufacturer
National Semiconductor
Series
LMP®r
Datasheet

Specifications of LMP7701MF/NOPB

Amplifier Type
General Purpose
Number Of Circuits
1
Output Type
Rail-to-Rail
Slew Rate
1.1 V/µs
Gain Bandwidth Product
2.5MHz
Current - Input Bias
0.2pA
Voltage - Input Offset
37µV
Current - Supply
790µA
Current - Output / Channel
86mA
Voltage - Supply, Single/dual (±)
2.7 V ~ 12 V, ±1.35 V ~ 6 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
SOT-23-5, SC-74A, SOT-25
Number Of Channels
1
Voltage Gain Db
130 dB
Common Mode Rejection Ratio (min)
88 dB
Input Voltage Range (max)
12 V
Input Voltage Range (min)
2.7 V
Input Offset Voltage
0.2 mV at 5 V
Output Current (typ)
42 mA
Operating Supply Voltage
3 V, 5 V, 9 V
Supply Current
1 mA at 5 V
Maximum Operating Temperature
+ 125 C
Mounting Style
SMD/SMT
Minimum Operating Temperature
- 40 C
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
-3db Bandwidth
-
Lead Free Status / Rohs Status
 Details
Other names
LMP7701MF
LMP7701MFTR
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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