LMC6001BIN National Semiconductor, LMC6001BIN Datasheet - Page 10

• Manufacturer Part Number: LMC6001BIN
• Description: IC, OP-AMP, 1.3MHZ, 1.5V/µs, DIP-8
• Manufacturer: National Semiconductor

Specifications of LMC6001BIN

• Op Amp Type: Low Power
• No. Of Amplifiers: 1
• Bandwidth: 1.3MHz
• Slew Rate: 1.5V/µs
• Supply Voltage Range: 4.5V To 15.5V
• Amplifier Case Style: DIP
• No. Of Pins: 8
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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latchup mode. Limiting current to the supply pins will also in-
hibit latchup susceptibility.
Typical Applications
The extremely high input resistance, and low power con-
sumption, of the LMC6001 make it ideal for applications that
require battery-powered instrumentation amplifiers. Exam-
ples of these types of applications are hand-held pH probes,
analytic medical instruments, electrostatic field detectors and
gas chromotographs.
TWO OPAMP, TEMPERATURE
COMPENSATED pH PROBE AMPLIFIER
The signal from a pH probe has a typical resistance between
10 MΩ and 1000 MΩ. Because of this high value, it is very
important that the amplifier input currents be as small as pos-
sible. The LMC6001 with less than 25 fA input current is an
ideal choice for this application.
The theoretical output of the standard Ag/AgCl pH probe is
59.16 mV/pH at 25°C with 0V out at a pH of 7.00. This output
is proportional to absolute temperature. To compensate for
this, a temperature compensating resistor, R1, is placed in the
feedback loop. This cancels the temperature dependence of
the probe. This resistor must be mounted where it will be at
the same temperature as the liquid being measured.
The LMC6001 amplifies the probe output providing a scaled
voltage of ±100 mV/pH from a pH of 7. The second opamp, a
Note 12: (Micro-ohm style 137 or similar)
ULTRA-LOW INPUT CURRENT INSTRUMENTATION
AMPLIFIER
Figure 8
differential and common mode input resistance (>10
0.01% gain accuracy at A
MΩ imbalance in source resistance. Input current is less than
R1 100k + 3500 ppm/°C
R2 68.1k
R3, 8 5k
R4, 9 100k
R5 36.5k
R6 619k
R7 97.6k
D1 LM4040D1Z-2.5
C1 2.2 μF
shows an instrumentation amplifier that features high
(Note
V
= 1000, excellent CMRR with 1
12)
FIGURE 7. pH Probe Amplifier
14
Ω),
10
micropower LMC6041 provides phase inversion and offset so
that the output is directly proportional to pH, over the full range
of the probe. The pH reading can now be directly displayed
on a low cost, low power digital panel meter. Total current
consumption will be about 1 mA for the whole system.
The micropower dual operational amplifier, LMC6042, would
optimize power consumption but not offer these advantages:
1.
2.
The setup and calibration is simple with no interactions to
cause problems.
1.
2.
20 fA and offset drift is less than 2.5 μV/°C. R
simple means of adjusting gain over a wide range without de-
grading CMRR. R
without using super precision matched resistors. For good
CMRR over temperature, low drift resistors should be used.
The LMC6001A guarantees a 25 fA limit on input current
at 25°C.
The input ESD protection diodes in the LMC6042 are
only rated at 500V while the LMC6001 has much more
robust protection that is rated at 2000V.
Disconnect the pH probe and with R3 set to about mid-
range and the noninverting input of the LMC6001
grounded, adjust R8 until the output is 700 mV.
Apply −414.1 mV to the noninverting input of the
LMC6001. Adjust R3 for and output of 1400 mV. This
completes the calibration. As real pH probes may not
perform exactly to theory, minor gain and offset
adjustments should be made by trimming while
measuring a precision buffer solution.
7
is an initial trim used to maximize CMRR
1188715
2
provides a