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TC7117 Folha de dados(PDF) 9 Page - Microchip Technology |
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TC7117 Folha de dados(HTML) 9 Page - Microchip Technology |
9 / 26 page 2002-2012 Microchip Technology Inc. DS21457D-page 9 TC7116/A/TC7117/A 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 ( 15), 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 shown in Figure 3-2. FIGURE 3-2: Using an External Reference Analog common is also used as VIN- return during auto-zero and de-integrate. If VIN- is different from ana- log 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, VIN- 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 conve- niently 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 30mA 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). How- ever, there is only 10 A of source current, so analog common may easily be tied to a more negative voltage, thus overriding the internal reference. 3.1.7 TEST The TEST pin serves two functions. On the TC7117/ TC7117A, it is coupled to the internally generated digi- tal supply through a 500 resistor. Thus, it can be used as a negative supply for externally generated segment drivers, such as decimal points, or any other presenta- tion the user may want to include on the LCD. (Figure 3-3 and Figure 3-4 show such an application.) No more than a 1mA load should be applied. The second function is a “lamp test.” When TEST is pulled HIGH (to V+), all segments will be turned ON and the display should read -1888. The TEST pin will sink about 10mA under these conditions. FIGURE 3-3: Simple Inverter for Fixed Decimal Point V+ V+ 1.2V REF COMMON TC7116 TC7116A TC7117 TC7117A 6.8k Ω VREF+ 20k Ω TC7116 TC7116A BP TEST 37 21 V+ V+ GND To LCD Decimal Point To LCD Backplane 4049 |
Nº de peça semelhante - TC7117 |
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Descrição semelhante - TC7117 |
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