TC901 Просмотр технического описания (PDF) - TelCom Semiconductor Inc => Microchip
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TC901 Datasheet PDF : 4 Pages
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MONOLITHIC, AUTO-ZEROED
OPERATIONAL AMPLIFIER
1
TC901
Overload Recovery
The TC901 recovers quickly from output saturation.
Typical recovery time from positive output saturation is 20
msec. Negative output saturation recovery time is typically
5 msec.
Thermocouple Errors
Heating a junction made from two different metallic
wires causes current flow. This is known as the Seebeck
effect. An open-circuit voltage (Seebeck voltage) can be
measured across the junction. 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 TC901's offset voltage drift.
Unless unwanted thermocouple potentials can be con-
trolled, system performance will be less than optimum.
Unwanted thermocouple junctions are created when
leads are soldered or sockets/connectors are used. Low
thermoelectric coefficient solder can reduce errors. A 60%
Cd/40% Sn Pb solder has one-tenth 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 junctions are
kept at the same temperature, their summation will add to
zero, canceling errors (Figure 7).
Shielding precision analog circuits from air currents —
especially those caused by power dissipating components
and fans — will minimize temperature gradients and mini-
mize thermocouple-induced errors.
J3 = J4
J2 = J5
J1 = J6
NO TEMPERATURE DIFFERENTIAL
AND SAME METALLIC CONNECTION
J2
J1
J3
PACKAGE
PIN
J4
J6
–
J3 V3
+
+
J4 V4
–
J5
J2
+–
V2
J1
+–
V1
VT = V1 + V2 + V3 – V4 – V5 – V6 = 0
+ V5 –
J5
+ V6 –
J6
VT = 0
Figure 7. Unwanted Thermocouple Errors Eliminated by Reducing
Thermal Gradients and Balancing Junctions
Avoiding Latch-Up
Junction-isolated CMOS circuits inherently contain a
parasitic p-n-p-n transistor circuit. Voltages exceeding the
supplies by 0.3V should not be applied to the device pins.
TELCOM SEMICONDUCTOR, INC.
Larger voltages can turn the p-n-p-n device on, causing
2 excessive device power supply current and excessive power
dissipation. TC901's power supply should be established at
the same time (or before) input signals are applied. If this is
not possible, input current should be limited to 100µA to
avoid triggering the p-n-p-n structure.
Pin Compatibility
The CMOS TC901 is pin compatible with other chopper-
3 stabilized amplifiers, such as the 7650, 7652 and 1052.
Amplifiers such as the 7650 require 0.1µF external capaci-
tors connected to pins 1 and 8. The TC901 includes the
chopper capacitors on-chip, so external capacitors are not
required. Since pins 1, 5 and 8 of the TC901 are not
connected, the TC901 can directly replace other chopper-
stabilized amplifiers in existing circuits.
4 The TC901 pinout also matches many popular bipolar
and JFET op amps, such as the OP-07, OP-20, LM101,
LM108, 356 and 741. In many applications that operate from
±15V power supplies, the TC901 offers superior electrical
performance and is a functional pin-compatible replace-
ment. Offset voltage correction potentiometers, compensa-
tion capacitors, and chopper-stabilization capacitors can be
removed when retrofitting existing equipment designs.
System parts count, assembly time, and system cost are
reduced, while reliability and performance are improved.
5
Overload Recovery
The TSC90X Series recovers quickly from output
saturation. Typical recovery time from positive output satu-
ration is 20 msec. Negative output saturation recovery time
is typically 5 msec.
6
7
8
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