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Zakładka z wyszukiwarką danych komponentów |
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Zakładka z wyszukiwarką danych komponentów |
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TC7650CPA Arkusz danych(PDF) 7 Page - Microchip Technology |
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TC7650CPA Arkusz danych(HTML) 7 Page - Microchip Technology |
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7 / 14 page  © 2002 Microchip Technology Inc. DS21463B-page 7 TC7650 3.9 Pin Compatibility On the 8-pin mini-DIP TC7650, the external null stor- age capacitors are connected to pins 1 and 8. On most other operational amplifiers these are left open or are used for offset potentiometer or compensation capaci- tor connections. For OP05 and OP07 operational amplifiers, the replacement of the offset null potentiometer between pins 1 and 8 by two capacitors from the pins to VSS will convert the OP05/07 pin configurations for TC7650 operation. For LM108 devices, the compensation capacitor is replaced by the external nulling capacitors. The LM101/748/709 pinouts are modified similarly by removing any circuit connections to Pin 5. On the TC7650, Pin 5 is the output clamp connection. Other operational amplifiers may use this pin as an off- set or compensation point. The minor modifications needed to retrofit a TC7650 into existing sockets operating at reduced power sup- ply voltages make prototyping and circuit verification straightforward. 3.10 Input Guarding High impedance, low leakage CMOS inputs allow the TC7650 to make measurements of high-impedance sources. Stray leakage paths can increase input cur- rents and decrease input resistance unless inputs are guarded. A guard is a conductive PC trace surrounding the input terminals. The ring connects to a low imped- ance point at the same potential as the inputs. Stray leakages are absorbed by the low impedance ring. The equal potential between ring and inputs prevents input leakage currents. Typical guard connections are shown in Figure 3-6. The 14-pin DIP configuration has been specifically designed to ease input guarding. The pins adjacent to the inputs are unused. In applications requiring low leakage currents, boards should be cleaned thoroughly and blown dry after sol- dering. Protective coatings will prevent future board contamination. 3.11 Component Selection The two required capacitors, CA and CB, have optimum values, depending on the clock or chopping frequency. For the preset internal clock, the correct value is 0.1 µF. To maintain the same relationship between the chop- ping frequency and the nulling time constant, the capacitor values should be scaled in proportion to the external clock, if used. High quality film type capacitors (such as Mylar) are preferred; ceramic or other lower grade capacitors may be suitable in some applications. For fast settling on initial turn-on, low dielectric absorp- tion capacitors (such as polypropylene) should be used. With ceramic capacitors, several seconds may be required to settle to 1 µV. FIGURE 3-6: INPUT GUARD CONNECTION Input Output R2 Inverting Amplifier Input Output Follower Input Output R2 R1 Noninverting Amplifier R3* R3* Should Be Low Impedence For Optimum Guarding NOTE: R3 = R1 R2 R1 + R2 R3* R1 |
Podobny numer części - TC7650CPA |
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Podobny opis - TC7650CPA |
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