TC911A/TC911B
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in <Blue
performance and can be a functional pin compatible
replacement. Offset voltage correction potentiometers,
compensation capacitors, and chopper stabilization
capacitors can be removed when retro-fitting existing
equipment designs.
TABLE 2-1:
Pin Number
1, 5, 8
2
3
4
6
7
PIN FUNCTION TABLE
3.2
Symbol
NC
-INPUT
+INPUT
V
SS
OUTPUT
V
DD
Description
No Internal Connection.
Inverting Input
Non-inverting Input
Negative Power Supply
Output
Positive Power Supply
Thermocouple Errors
3.0
3.1
DETAILED DESCRIPTION
Pin Compatibility
Heating one joint of a loop made from two different
metallic wires causes current flow. This is known as the
Seebeck effect. By breaking the loop, an open circuit
voltage (Seebeck voltage) can be measured. Junction
temperature and metal type determine the magnitude.
Typical values are 0.1μV/°C to 10μV/°C. Thermal
induced voltages can be many times larger than the
TC911 offset voltage drift. Unless unwanted thermo-
couple potentials can be controlled, system perfor-
mance will be less than optimum.
Unwanted thermocouple junctions are created when
leads are soldered or sockets/connectors are used.
Low thermo-electric coefficient solder can reduce
errors. A 60% Sn/36% Pb solder has 1/10 the thermal
voltage of common 64% Sn/36% Pb solder at a copper
junction.
The number and type of dissimilar metallic junctions in
the input circuit loop should be balanced. If the junc-
tions are kept at the same temperature, their summa-
tion will add to zero-canceling errors (Figure 3-1).
Shielding precision analog circuits from air currents -
especially those caused by power dissipating compo-
nents and fans - will minimize temperature gradients
and thermocouple induced errors.
The CMOS TC911 is pin compatible with the industry
standard ICL7650 chopper stabilized amplifier. The
ICL7650 must use external 0.1μF capacitors con-
nected at pins 1 and 8.
With the TC911, external off-
set voltage error canceling capacitors are not
required.
On the TC911 pins 1, 8 and 5 are not con-
nected internally. The ICL7650 uses pin 5 as an
optional output clamp connection. External chopper
capacitors and clamp connections are not necessary
with the TC911. External circuits connected to pins 1, 8
and 5 will have no effect. The TC911 can be quickly
evaluated in existing ICL7650 designs. Since external
capacitors are not required, system part count, assem-
bly time and total system cost are reduced. Reliability
is increased and PC board layout eased by having the
error storage capacitors integrated on the TC911 chip.
The TC911 pinout matches many existing op amps:
741, LM101, LM108, OP05–OP08, OP-20, OP-21,
ICL7650 and ICL7652. In many applications operating
from +5V supplies, the TC911 offers superior electrical
FIGURE 3-1:
UNWANTED THERMOCOUPLE ERRORS ELIMINATED BY REDUCING
THERMAL GRADIENTS AND BALANCING JUNCTIONS
J
3
= J
4
J
2
= J
5
No Temperature Differential and same
J
1
= J
6
Metallic Connection
J
2
J
1
J
3
J
2
Package –
Pin
J3 V
3
+
+
J4 V
4
–
+
V
2
–
+
J
1
V
1
–
V
T
= V
1
+ V
2
+ V
3
– V
4
– V
5
– V
6
= 0
J
4
J
5
J
6
V
T
= 0
+
V
5
J
5
–
+
V
6
J
6
–
DS21481C-page 4
©
2005 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
