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TC911BCOA Scheda tecnica(PDF) 4 Page - Microchip Technology |
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TC911BCOA Scheda tecnica(HTML) 4 Page - Microchip Technology |
4 / 14 page TC911A/TC911B DS21481C-page 4 © 2005 Microchip Technology Inc. 2.0 PIN DESCRIPTIONS The descriptions of the pins are listed in <Blue References>Table 2-1. TABLE 2-1: PIN FUNCTION TABLE 3.0 DETAILED DESCRIPTION 3.1 Pin Compatibility The CMOS TC911 is pin compatible with the industry standard ICL7650 chopper stabilized amplifier. The ICL7650 must use external 0.1 μF 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 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. 3.2 Thermocouple Errors 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 0.1 μV/°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. FIGURE 3-1: UNWANTED THERMOCOUPLE ERRORS ELIMINATED BY REDUCING THERMAL GRADIENTS AND BALANCING JUNCTIONS Pin Number Symbol Description 1, 5, 8 NC No Internal Connection. 2 -INPUT Inverting Input 3 +INPUT Non-inverting Input 4VSS Negative Power Supply 6 OUTPUT Output 7VDD Positive Power Supply J3 J4 J2 J1 J6 Package Pin J3 = J4 J2 = J5 J1 = J6 No Temperature Differential and same Metallic Connection + – – + +– +– +– +– V2 V1 V5 V6 V4 V3 J4 J3 J2 J1 J5 J5 J6 VT = 0 VT = V1 + V2 + V3 – V4 – V5 – V6 = 0 |
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