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TC14433ELI Datasheet(PDF) 7 Page - Microchip Technology |
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TC14433ELI Datasheet(HTML) 7 Page - Microchip Technology |
7 / 20 page © 2002 Microchip Technology Inc. DS21394B-page 7 TC14433/A 3.0 DETAILED DESCRIPTION The TC14433 CMOS IC becomes a modified dual- slope A/D with a minimum of external components. This IC has the customary CMOS digital logic circuitry, as well as CMOS analog circuitry. It provides the user with digital functions such as (counters, latches, multiplexers), and analog functions such as (operational amplifiers and comparators) on a single chip. Refer to the Functional Block diagram, Figure 3-3 Features of the TC14433/A include auto-zero, high input impedances and auto-polarity. Low power consumption and a wide range of power supply volt- ages are also advantages of this CMOS device. The system's auto-zero function compensates for the offset voltage of the internal amplifiers and comparators. In this "ratiometric system," the output reading is the ratio of the unknown voltage to the reference voltage, where a ratio of 1 is equal to the maximum count of 1999. It takes approximately 16,000 clock periods to complete one conversion cycle. Each conversion cycle may be divided into 6 segments. Figure 3-1 shows the conver- sion cycle in 6 segments for both positive and negative inputs. FIGURE 3-1: INTEGRATOR WAVEFORMS AT PIN 6 Segment 1 - The offset capacitor (CO), which compen- sates for the input offset voltages of the buffer and inte- grator amplifiers, is charged during this period. However, the integrator capacitor is shorted. This segment requires 4000 clock periods. Segment 2 - During this segment, the integrator output decreases to the comparator threshold voltage. At this time, a number of counts equivalent to the input offset voltage of the comparator is stored in the offset latches for later use in the auto-zero process. The time for this segment is variable and less than 800 clock periods. Segment 3 - This segment of the conversion cycle is the same as Segment 1. Segment 4 - Segment 4 is an up going ramp cycle with the unknown input voltage (VX as the input to the integrator. Figure 4-2 shows the equivalent configuration of the analog section of the TC14433. The actual configuration of the analog section is dependent upon the polarity of the input voltage during the previous conversion cycle. FIGURE 3-2: EQUIVALENT CIRCUIT DIAGRAMS OF THE ANALOG SECTION DURING SEGMENT 4 OF THE TIMING CYCLE Segment 5 - This segment is a down-going ramp period with the reference voltage as the input to the integrator. Segment 5 of the conversion cycle has a time equal to the number of counts stored in the offset storage latches during Segment 2. As a result, the sys- tem zeros automatically. Segment 6 - This is an extension of Segment 5. The time period for this portion is 4000 clock periods. The results of the A/D conversion cycle are determined in this portion of the conversion cycle. Start 1 2 3 4 5 6 Typical Positive Input Voltage Typical Negative Input Voltage Time Segment Number End VX VX C1 Comparator R1 Buffer Integrator + – + – + – VX |
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