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TC9400EJD Arkusz danych(PDF) 8 Page - Microchip Technology |
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TC9400EJD Arkusz danych(HTML) 8 Page - Microchip Technology |
8 / 20 page TC9400/9401/9402 DS21483B-page 8 © 2002 Microchip Technology Inc. 3.2 Voltage-to-Time Measurements The TC9400 output can be measured in the time domain as well as the frequency domain. Some micro- computers, for example, have extensive timing capabil- ity, but limited counter capability. Also, the response time of a time domain measurement is only the period between two output pulses, while the frequency mea- surement must accumulate pulses during the entire counter time-base period. Time measurements can be made from either the TC9400's PULSE FREQ OUT output, or from the FREQ/2 OUT output. The FREQ/2 OUT output changes state on the rising edge of PULSE FREQ OUT, so FREQ/2 OUT is a symmetrical square wave at one-half the pulse output frequency. Timing measure- ments can, therefore, be made between successive PULSE FREQ OUT pulses, or while FREQ/2 OUT is high (or low). 4.0 PIN FUNCTIONS 4.1 Threshold Detector Input In the V/F mode, this input is connected to the AMPLI- FIER OUT output (Pin 12) and triggers a 3 µsec pulse when the input voltage passes through its threshold. In the F/V mode, the input frequency is applied to this input. The nominal threshold of the detector is half way between the power supplies, or (VDD +VSS)/2 ±400mV. The TC9400's charge balancing V/F technique is not dependent on a precision comparator threshold, because the threshold only sets the lower limit of the Op Amp output. The Op Amp's peak-to-peak output swing, which determines the frequency, is only influenced by external capacitors and by VREF. 4.2 Pulse Freq Out This output is an open drain N-channel FET, which pro- vides a pulse waveform whose frequency is propor- tional to the input voltage. This output requires a pull- up resistor and interfaces directly with MOS, CMOS, and TTL logic (see Figure 4-1). FIGURE 4-1: OUTPUT WAVEFORMS 3 µsec Typ. 1/f FOUT FOUT/2 Amp Out VREF 0V CREF CINT Notes: 1. To adjust FMIN, set VIN = 10mV and adjust the 50kΩ offset for 10Hz output. 2. To adjust FMAX, set VIN = 10V and adjust RIN or VREF for 10kHz output. 3. To increase FOUTMAX to 100kHz, change CREF to 2pF and CINT to 75pF. 4. For high performance applications, use high stability components for RIN, CREF, VREF (metal film resistors and glass capacitors). Also, separate output ground (Pin 9) from input ground (Pin 6). |
Podobny numer części - TC9400EJD |
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Podobny opis - TC9400EJD |
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