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TC7136CKW датащи(PDF) 9 Page - TelCom Semiconductor, Inc |
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TC7136CKW датащи(HTML) 9 Page - TelCom Semiconductor, Inc |
9 / 12 page 3-255 TELCOM SEMICONDUCTOR, INC. 7 6 5 4 3 1 2 8 Component Value Nominal Full-Scale Voltage 200mV 2V CAZ 0.47 µF 0.1 µF RINT 180 k Ω 1.8 M Ω CINT 0.047 µF 0.047 µF NOTE:fOSC = 48 kHz (3 readings per sec). ROSC = 180kΩ, COSC = 50 output voltage back to zero during the reference integrate phase, is stored on CREF. A 0.1 µF capacitor is acceptable when V – REF is tied to analog common. If a large common- mode voltage exists (V – REF ≠ analog common) and the application requires a 200 mV full scale, increase CREF to 1 µF. Roll-over error will be held to less than 0.5 count. A Mylar-type dielectric capacitor is adequate. Integrating Capacitor (CINT) CINT should be selected to maximize integrator output voltage swing without causing output saturation. Analog common will normally supply the differential voltage refer- ence this case, a ±2V full-scale integrator output swing is satisfactory. For 3 readings per second (fOSC = 48 kHz) a 0.047 µF value is suggested. For one reading per second, 0.15 µF is recommended. If a different oscillator frequency is used, CINT must be changed in inverse proportion to maintain the nominal ±2V integrator swing. An exact expression for CINT is: Oscillator Components COSC should be 50 pF. ROSC is selected from the equation: fOSC = . Note that fOSC is 4 to generate the TC7136A's internal clock. The backplane drive signal is derived by dividing fOSC by 800. To achieve maximum rejection of 60Hz noise pickup, the signal integrate period should be a multiple of 60Hz. Oscillator frequencies of 240kHz, 120kHz, 80kHz, 60kHz, 40kHz, etc. should be selected. For 50 Hz rejection, oscil- lator frequencies of 200kHz, 100kHz, 66-2/3 kHz, 50kHz, 40kHz, etc. would be suitable. Note that 40kHz (2.5 read- ings per second) will reject both 50Hz and 60Hz. Reference Voltage Selection A full-scale reading (2000 counts) requires the input signal be twice the reference voltage. 0.45 RC In some applications, a scale factor other than unity may exist between a transducer output voltage and the required digital reading. Assume, for example, a pressure transducer output for 2000 lb/in.2 is 400 mV. Rather than dividing the input voltage by two, the reference voltage should be set to 200 mV. This permits the transducer input to be used directly. The differential reference can also be used when a digital zero reading is required when VIN is not equal to zero. This is common in temperature measuring instrumentation. A compensating offset voltage can be applied between analog common and V – IN The transducer output is connected between V + IN and analog common. DEVICE PIN FUNCTIONAL DESCRIPTION Differential Signal Inputs V + IN (Pin 31), V – IN (Pin 30) The TC7136/A is designed with true differential inputs and accepts input signals within the input stage common- mode voltage range (VCM). The typical range is V+ –1V to V– +1V. Common-mode voltages are removed from the system when the TC7136A operates from a battery or floating power source (isolated from measured system), and VIN – is con- nected to analog common (VCOM). (See Figure 7.) Required Full-Scale Voltage* VREF 200 mV 100 mV 2V 1V *VFS = 2 VREF. where: fOSC = Clock frequency at pin 38 VFS = Full-scale input voltage RINT = Integrating resistor VINT = Desired full-scale integrator output swing. CINT must have low dielectric absorption to minimize roll-over error. A polypropylene capacitor is recommended. Integrating Resistor (RINT) The input buffer amplifier and integrator are designed with Class A output stages. The output stage idling current is 6 µA. The integrator and buffer can supply 1 µA drive currents with negligible linearity errors. RINT is chosen to remain in the output stage linear drive region, but not so large that PC board leakage currents induce errors. For a 200 mV full scale, RINT is 180 kΩ. A 2V full scale requires 1.8 M Ω. CINT =, 1 fOSC ( VFS RINT ( ) ) (4000) VINT LOW POWER, 3-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTERS TC7136 TC7136A |
Аналогичный номер детали - TC7136CKW |
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Аналогичное описание - TC7136CKW |
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