Datenblatt-Suchmaschine für elektronische Bauteile |
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TC7106CKW Datenblatt(PDF) 11 Page - TelCom Semiconductor, Inc |
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TC7106CKW Datenblatt(HTML) 11 Page - TelCom Semiconductor, Inc |
11 / 19 page 3-193 TELCOM SEMICONDUCTOR, INC. 7 6 5 4 3 1 2 8 Oscillator Components ROSC (Pin 40 to Pin 39) should be 100kΩ. COSC is selected using the equation: For fOSC of 48kHz, COSC is 100pF nominally. Note that fOSC is divided by four to generate the TC7106A internal control 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, 48kHz, 40kHz, etc. should be selected. For 50 Hz rejection, oscillator frequencies of 200kHz, 100kHz, 66 2/3kHz, 50kHz, 40kHz, etc. would be suitable. Note that 40kHz (2.5 read- ings/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. Required Full-Scale Voltage* VREF 200.0mV 100.0mV 2.000V 1.000V * VFS = 2 VREF 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 is 400mV for 2000 lb/in2. Rather than dividing the input voltage by two the reference voltage should be set to 200mV. 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 con- nected between V+IN and analog common. The internal voltage reference potential available at analog common will normally be used to supply the convert- er's reference. This potential is stable whenever the supply potential is greater than approximately 7V. In applications where an externally-generated reference voltage is desired, refer to Figure 7. fOSC = 0.45 RC Integrating Capacitor – CINT CINT should be selected to maximize the integrator output voltage swing without causing output saturation. Due to the TC7106A/7107A superior temperature coefficient specification, analog common will normally supply the differ- ential voltage reference. For this case a ±2V full-scale integrator output swing is satisfactory. For 3 readings/ second (fOSC = 48kHz) a 0.22µF value is suggested. If a different oscillator frequency is used, CINT must be changed in inverse proportion to maintain the nominal ±2 V integrator swing. An exact expression for CINT is: CINT = VINT 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 rollover 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 100 µA. The integrator and buffer can supply 20µA drive currents with negligible linearity errors. RINT is chosen to remain in the output stage linear drive region but not so large that printed circuit board leakage currents induce errors. For a 200mV full-scale, RINT is 47kΩ. 2.0V full-scale requires 470k Ω. Component Nominal Full-Scale Voltage Value 200.0mV 2.000V CAZ 0.47 µF 0.047 µF RINT 47k Ω 470k Ω CINT 0.22 µF 0.22 µF Note:1. fOSC = 48kHz (3 readings/sec) VFS RINT 1 fOSC (4000) ( ) ( ) TC7106 TC7106A TC7107 TC7107A 3-1/2 DIGIT A/D CONVERTERS |
Ähnliche Teilenummer - TC7106CKW |
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Ähnliche Beschreibung - TC7106CKW |
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