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TC7117ACKW Datasheet(PDF) 8 Page - TelCom Semiconductor, Inc |
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TC7117ACKW Datasheet(HTML) 8 Page - TelCom Semiconductor, Inc |
8 / 14 page 3-210 TELCOM SEMICONDUCTOR, INC. TC7116 TC7116A BP TEST 37 21 V+ V+ GND TO LCD DECIMAL POINT TO LCD BACK- PLANE 4049 V+ REF V+ 1.2V REF COMMON TC7116 TC7116A TC7117 TC7117A 6.8 k Ω V+ TC9491CZM Ω 20 k Figure 4. Using an External Reference recommended 2V full-scale swing with little loss of accu- racy. The integrator output can swing within 0.3V of either supply without loss of linearity. 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 voltage will have a low voltage coefficient (0.001%/ %), low output impedance ( ≅15Ω), and a temperature coef- ficient of less than 20 ppm/ °C, typically, and 50 ppm maxi- mum. The TC7116/TC7117 temperature coefficients are typically 80 ppm/ °C. An external reference may be used, if necessary, as shown in Figure 4. Analog common is also used as V – IN return during auto- zero and deintegrate. If V – IN is different from analog common, a common-mode voltage exists in the system and is taken care of by the excellent CMRR of the converter. However, in some applications, V – IN will be set at a fixed, known voltage (power supply common for instance). In this application, analog common should be tied to the same point, thus removing the common-mode voltage from the converter. The same holds true for the reference voltage; if it can be conveniently referenced to analog common, it should be. This removes the common-mode voltage from the reference system. Within the IC, analog common is tied to an N-channel FET that can sink 30 mA or more of current to hold the voltage 3V below the positive supply (when a load is trying to pull the analog common line positive). However, there is only 10 µA of source current, so analog common may easily be tied to a more negative voltage, thus overriding the internal reference. TEST The TEST pin serves two functions. On the TC7117/ TC7117A, it is coupled to the internally-generated digital supply through a 500 Ω resistor. Thus, it can be used as a Figure 7. Clock Circuits TC7116/TC7116A TC7117/TC7117A TO COUNTER CRYSTAL RC NETWORK 40 38 EXT OSC 39 TO TEST PIN ON TC7116/TC7116A TO GROUND PIN ON TC7117/TC7117A Figure 6. Exclusive “OR” Gate for Decimal Point Drive TC7116 TC7116A DECIMAL POINT SELECT V + V + TEST GND 4030 TO LCD DECIMAL POINTS BP Figure 5. Simple Inverter for Fixed Decimal Point 3-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTERS WITH HOLD TC7116 TC7116A TC7117 TC7117A |
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