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TC7116CLW Fiches technique(PDF) 8 Page - Microchip Technology |
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TC7116CLW Fiches technique(HTML) 8 Page - Microchip Technology |
8 / 22 page TC7116/A/TC7117/A DS21457B-page 8 © 2002 Microchip Technology Inc. FIGURE 3-1: ANALOG SECTION OF TC7116/TC7117A AND TC7117/TC7117A 3.1.3 REFERENCE INTEGRATE PHASE The final phase is reference integrate, or de-integrate. Input low is internally connected to analog common and input high is connected across the previously charged reference capacitor. Circuitry within the chip ensures that the capacitor will be connected with the correct polarity to cause the integrator output to return to zero. The time required for the output to return to zero is proportional to the input signal. The digital reading displayed is: EQUATION 3-1: 3.1.4 REFERENCE The positive reference voltage (VREF+) is referred to analog common. 3.1.5 DIFFERENTIAL INPUT This input can accept differential voltages anywhere within the Common mode range of the input amplifier or, specifically, from 1V below the positive supply to 1V above the negative supply. In this range, the system has a CMRR of 86dB, typical. However, since the inte- grator also swings with the Common mode voltage, care must be exercised to ensure that the integrator output does not saturate. A worst case condition would be a large, positive Common mode voltage with a near full scale negative differential input voltage. The nega- tive input signal drives the integrator positive, when most of its swing has been used up by the positive Common mode voltage. For these critical applications, the integrator swing can be reduced to less than the recommended 2V full scale swing with little loss of accuracy. The integrator output can swing within 0.3V of either supply without loss of linearity. 3.1.6 ANALOG COMMON This pin is included primarily to set the Common mode voltage for battery operation (TC7116/TC7116A), or for any system where the input signals are floating, with respect to the power supply. The analog common pin sets a voltage approximately 2.8V more negative than the positive supply. This is selected to give a minimum end of life battery voltage of about 6V. However, analog common has some attributes of a reference voltage. When the total supply voltage is large enough to cause the zener to regulate (>7V), the analog common volt- age will have a low voltage coefficient (0.001%), low output impedance ( ≅15Ω), and a temperature coeffi- cient of less than 20ppm/°C, typically, and 50 ppm max- imum. The TC7116/TC7117 temperature coefficients are typically 80ppm/°C. An external reference may be used, if necessary, as shownin Figure3-2. FIGURE 3-2: USING AN EXTERNAL REFERENCE TC7116 TC7116A TC7117 TC7117A CREF CREF+ CREF- RINT V+ CAZ Auto-Zero VINT 28 35 29 27 33 36 34 10 µA 31 AZ AZ INT AZ & DE (±) 32 30 INT 26 Integrator V+ -3V Comparator To Digital Section DE (+) DE (–) DE (+) DE (–) V+ AZ Analog Common VIN+ VIN- VBUFF CINT VREF+ Low Temp. Drift Zener VREF V- + – + – + + – 1000 = VIN VREF V+ V+ 1.2V REF COMMON TC7116 TC7116A TC7117 TC7117A 6.8k Ω VREF+ 20k Ω |
Numéro de pièce similaire - TC7116CLW |
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Description similaire - TC7116CLW |
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