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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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TC9402CPD 데이터시트(PDF) 10 Page - Microchip Technology |
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TC9402CPD 데이터시트(HTML) 10 Page - Microchip Technology |
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10 / 20 page  TC9400/9401/9402 DS21483B-page 10 © 2002 Microchip Technology Inc. 5.0 VOLTAGE-TO-FREQUENCY (V/F) CONVERTER DESIGN INFORMATION 5.1 Input/Output Relationships The output frequency (FOUT) is related to the analog input voltage (VIN) by the transfer equation: EQUATION 5-1: 5.2 External Component Selection 5.2.1 RIN The value of this component is chosen to give a full scale input current of approximately 10 µA: EQUATION 5-2: EQUATION 5-3: Note that the value is an approximation and the exact relationship is defined by the transfer equation. In prac- tice, the value of RIN typically wouldbetrimmedto obtain full scale frequency at VIN full scale (see Section 5.3, Adjustment Procedure). Metal film resis- tors with 1% tolerance or better are recommended for high accuracy applications because of their thermal stability and low noise generation. 5.2.2 CINT The exact value is not critical but is related to CREF by the relationship: 3CREF ≤ CINT ≤ 10CREF Improved stability and linearity are obtained when CINT ≤ 4CREF. Low leakage types are recommended, although mica and ceramic devices can be used in applications where their temperature limits are not exceeded. Locate as close as possible to Pins 12 and 13. 5.2.3 CREF Theexact valueisnot critical and maybeusedtotrim the full scale frequency (see Section 7.1, Input/Output Relationships). Glass film or air trimmer capacitors are recommended because of their stability and low leak- age. Locate as close as possible to Pins 5 and 3 (see Figure 5-1). FIGURE 5-1: RECOMMENDED CREF VS. VREF 5.2.4 VDD,VSS Power supplies of ±5V are recommended. For high accuracy requirements, 0.05% line and load regulation and 0.1 µF disc decoupling capacitors, located near the pins, are recommended. 5.3 Adjustment Procedure Figure 3-1 shows a circuit for trimming the zero loca- tion. Full scale may be trimmed by adjusting RIN,VREF, or CREF. Recommended procedure for a 10kHz full scale frequency is as follows: 1. Set VIN to 10mV and trim the zero adjust circuit to obtain a 10Hz output frequency. 2. Set VIN to 10V and trim either RIN,VREF,or CREF to obtain a 10kHz output frequency. If adjustments are performed in this order, there should be no interaction and they should not have to be repeated. 5.4 Improved Single Supply V/F Converter Operation A TC9400, which operates from a single 12 to 15V vari- able power source, is shown in Figure 5-2. This circuit uses two Zener diodes to set stable biasing levels for the TC9400. The Zener diodes also provide the refer- ence voltage, so the output impedance and tempera- ture coefficient of the Zeners will directly affect power supply rejection and temperature performance. Full scale adjustment is accomplished by trimming the input current. Trimming the reference voltage is not recom- mended for high accuracy applications unless an Op Amp is used as a buffer, because the TC9400 requires a low impedance reference (see Section 4.9, VREF pin description, for more information). The circuit of Figure 5-2 will directly interface with CMOS logic operating at 12V to 15V. TTL or 5V CMOS logic can be accommodated by connecting the output pull-up resistors to the +5V supply. An optoisolator can also be used if an isolated output is required; also, see Figure 5-3. Frequency Out = VIN RIN ,x 1 (VREF)(VREF) VIN FULLSCALE 10 µA RIN ≅ 10V 10 µA RIN ≅ =1M Ω 500 400 300 200 100 0 -1 -2 -3 -4 -5 -6 -7 VREF (V) 10kHz 100kHz VDD = +5V VSS = -5V RIN = 1MΩ VIN = +10V TA = +25°C |
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