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TC820CKW Folha de dados(PDF) 8 Page - Microchip Technology |
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TC820CKW Folha de dados(HTML) 8 Page - Microchip Technology |
8 / 28 page TC820 DS21476B-page 8 © 2002 Microchip Technology Inc. 3.0 DETAILED DESCRIPTION The TC820 is a 3-3/4 digit measurement system com- bining an integrating analog-to-digital converter, fre- quency counter, and logic level tester in a single package. The TC820 supersedes the TC7106 in new designs by improving performance and reducing sys- tem cost. The TC820 adds features that are difficult, expensive, or impossible to provide with older A/D con- verters (see Table 3-1). The high level of integration permits TC820 based instruments to deliver higher per- formance and more features, while actually reducing parts count. Fabricated in low power CMOS, the TC820 directly drives a 3-3/4 digit (3999 maximum) LCD. With a maximum range of 3999 counts, the TC820 pro- vides 10 times greater resolution in the 200mV to 400mV range than traditional 3-1/2 digit meters. An auto-zero cycle ensures a zero reading with a 0V input. CMOS processing reduces analog input bias current to only 1pA. Rollover error (the difference in readings for equal magnitude but opposite polarity input signals) is less than ±1 count. Differential reference inputs permit ratiometric measurements for ohms or bridge trans- ducer applications. The TC820's frequency counter option simplifies design of an instrument well-suited to both analog and digital troubleshooting: voltage, current, and resistance measurements, plus precise frequency measurements to 4MHz (higher frequencies can be measured with an external prescaler), and a simple logic probe. The fre- quency counter will automatically adjust its range to match the input frequency, over a four-decade range. Two logic level measurement inputs permit a TC820 based meter to function as a logic probe. When com- bined with external level shifters, the TC820 will display logic levels on the LCD and also turn on a piezoelectric buzzer when the measured logic level is low. Other TC820 features simplify instrument design and reduce parts count. On-chip decimal point drivers are included, as is a low battery detection annunciator. A piezoelectric buzzer can be controlled with an external switch or by the logic probe inputs. Two oscillator options are provided: a crystal can be used if high accu- racy frequency measurements are desired, or a simple RC option can be used for low-end instruments. A "peak reading hold" input allows the TC820 to retain the highest A/D or frequency reading. This feature is useful in measuring motor starting current, maximum temperature, and similar applications. A family of instruments can be created with the TC820. No additional design effort is required to create instru- ments with 3-3/4 digit resolution. The TC820 operates from a single 9V battery, with typ- ical power of 10mW. Packages include a 40-pin plastic DIP, 44-pin plastic flat package (PQFP), and 44-pin PLCC. TABLE 3-1: COMPETITIVE EVALUATION 3.1 General Theory of Operation 3.1.1 DUAL SLOPE CONVERSION PRINCIPLES The TC820 analog-to-digital converter operates on the principle of dual slope integration. An understanding of the dual slope conversion technique will aid the user in following the detailed TC820 theory of operation follow- ing this section. A conventional dual slope converter measurement cycle has two distinct phases: 1. Input Signal Integration 2. Reference Voltage Integration (De-integration) Referring to Figure 3-1, the unknown input signal to be converted is integrated from zero for a fixed time period (tINT), measured by counting clock pulses. A constant reference voltage of the opposite polarity is then inte- grated until the integrator output voltage returns to zero. The reference integration (de-integration) time (tDEINT) is then directly proportional to the unknown input voltage (VIN). Features Comparison TC820 7106 3-3/4 Digit Resolution Yes No Auto-Ranging Frequency Counter Yes No Logic Probe Yes No Decimal Point Drive Yes No Peak Reading Hold (Frequency or Voltage) Yes No Display Hold Yes No Simple 10:1 Range Change Yes No Buzzer Drive Yes No Low Battery Detection with Annunciator Yes No Over Range Detection with Annunciator Yes No Low Drift Reference Yes No Under Range/Over Range Logic Output Yes No Input Overload Display "OL" "1" LCD Annunciator Driver Yes No LCD Drive Type Triplexed Direct LCD Pin Connections 15 24 LCD Elements 36 23 |
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