Datenblatt-Suchmaschine für elektronische Bauteile |
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TC9402 Datenblatt(PDF) 7 Page - Microchip Technology |
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TC9402 Datenblatt(HTML) 7 Page - Microchip Technology |
7 / 24 page © 2006 Microchip Technology Inc. DS21483C-page 7 TC9400/9401/9402 3.0 DETAILED DESCRIPTION 3.1 Voltage-to-Frequency (V/F) Circuit Description The TC9400 V/F converter operates on the principal of charge balancing. The operation of the TC9400 is eas- ily understood by referring to Figure 3-1. The input volt- age (VIN) is converted to a current (IIN) by the input resistor. This current is then converted to a charge on the integrating capacitor and shows up as a linearly decreasing voltage at the output of the op amp. The lower limit of the output swing is set by the threshold detector, which causes the reference voltage to be applied to the reference capacitor for a time period long enough to charge the capacitor to the reference volt- age. This action reduces the charge on the integrating capacitor by a fixed amount (q = CREF x VREF), causing the op amp output to step up a finite amount. At the end of the charging period, CREF is shorted out. This dissipates the charge stored on the reference capacitor, so that when the output again crosses zero, the system is ready to recycle. In this manner, the con- tinued discharging of the integrating capacitor by the input is balanced out by fixed charges from the refer- ence voltage. As the input voltage is increased, the number of reference pulses required to maintain balance increases, which causes the output frequency to also increase. Since each charge increment is fixed, the increase in frequency with voltage is linear. In addi- tion, the accuracy of the output pulse width does not directly affect the linearity of the V/F. The pulse must simply be long enough for full charge transfer to take place. The TC9400 contains a “self-start” circuit to ensure the V/F converter always operates properly when power is first applied. In the event that, during power-on, the op amp output is below the threshold and CREF is already charged, a positive voltage step will not occur. The op amp output will continue to decrease until it crosses the -3.0V threshold of the “self-start” comparator. When this happens, an internal resistor is connected to the op amp input, which forces the output to go positive until the TC9400 is in its normal Operating mode. The TC9400 utilizes low-power CMOS processing for low input bias and offset currents, with very low power dissipation. The open drain N-channel output FETs provide high voltage and high current sink capability. FIGURE 3-1: 10 Hz to 10 kHz V/F Converter – + +5V +5V 14 VDD +5V RL 10 k Ω RL 10 k Ω 8 10 9 FOUT FOUT/2 11 3 μsec Delay Self- Start 12 5 20 k Ω 60 pF Op Amp CINT 820 pF CREF 180 pF 12 pF RIN 1M Ω VIN +5V -5V 50 k Ω 510 k Ω 10 k Ω 3 1 Offset Adjust IIN Zero Adjust 0V –10V IBIAS VSS 4 -5V 2 Output Common VREF OUT RBIAS 100 k Ω AMP OUT TC9400 TC9401 TC9402 GND 6 Threshold Detector Threshold Detect Reference Voltage (Typically -5V) ÷2 VREF 7 -3V INPUT |
Ähnliche Teilenummer - TC9402 |
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Ähnliche Beschreibung - TC9402 |
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