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TC9402 Fiches technique(PDF) 6 Page - TelCom Semiconductor, Inc |
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TC9402 Fiches technique(HTML) 6 Page - TelCom Semiconductor, Inc |
6 / 13 page 3-292 TELCOM SEMICONDUCTOR, INC. VOLTAGE-TO-FREQUENCY/ FREQUENCY-TO-VOLTAGE CONVERTERS TC9400 TC9401 TC9402 PIN FUNCTIONS Threshold Detector Input In the V/F mode, this input is connected to the amplifier 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 halfway be- tween 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. Pulse Freq Out This output is an open-drain N-channel FET which provides a pulse waveform whose frequency is proportional to the input voltage. This output requires a pull-up resistor and interfaces directly with MOS, CMOS, and TTL logic. Freq/2 Out This output is an open-drain N-channel FET which provides a square wave one-half the frequency of the pulse frequency output. The Freq/2 output will change state on the rising edge of Pulse Freq Out. This output requires a pull- up resistor and interfaces directly with MOS, CMOS, and TTL logic. 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. VOLTAGE-TO-TIME MEASUREMENTS The TC9400 output can be measured in the time do- main as well as the frequency domain. Some microcom- puters, for example, have extensive timing capability but limited counter capability. Also, the response time of a time domain measurement is only the period between two out- put pulses, while the frequency measurement must accu- mulate pulses during the entire counter timebase period. Time measurements can be made from either the TC9400's Pulse Freq Out output or from the Freq/2 output. The Freq/2 output changes state on the rising edge of Pulse Freq Out, so Freq/2 is a symmetrical square wave at one half the pulse output frequency. Timing measurements can therefore be made between successive Pulse Freq Out pulses, or while Freq/2 is high (or low). Figure 2 . 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 10 kHz output. 3. To increase fOUT MAX 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). |
Numéro de pièce similaire - TC9402 |
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Description similaire - TC9402 |
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