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TC9401 数据表(PDF) 10 Page - TelCom Semiconductor, Inc |
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TC9401 数据表(HTML) 10 Page - TelCom Semiconductor, Inc |
10 / 13 page 3-296 TELCOM SEMICONDUCTOR, INC. FREQUENCY-TO-VOLTAGE (F/V) CIRCUIT DESCRIPTION When used as an F/V converter, the TC9400 generates an output voltage linearly proportional to the input frequency waveform. Each zero crossing at the threshold detector's input causes a precise amount of charge (q = CREF × VREF) to be dispensed into the op amp's summing junction. This charge in turn flows through the feedback resistor, generating voltage pulses at the output of the op amp. A capacitor (CINT) across RINT averages these pulses into a DC voltage which is linearly proportional to the input frequency. F/V CONVERTER DESIGN INFORMATION Input/Output Relationships The output voltage is related to the input frequency (fIN) by the transfer equation: VOUT = [VREF CREF RINT] fIN. The response time to a change in fIN is equal to (RINT CINT). The amount of ripple on VOUT is inversely proportional to CINT and the input frequency. CINT can be increased to lower the ripple. Values of 1µF to 100 µF are perfectly acceptable for low frequencies. When the TC9400 is used in the single-supply mode, VREF is defined as the voltage difference between pin 7 and pin 2. +5V 14 64 +5V –5V VDD 1.0M 11 33k IN914 VSS DET TC9400 0.01 µF Frequency Input 0V GND +8V to +5V 14 10k 4 +5V VDD 1.0M 11 33k IN914 VSS DET TC9400 0.01 µF Frequency Input 0V 0.1 µF 10k (B) Single Supply (A) ±5V Supply Figure 6. Frequency Input Level Shifter Input Voltage Levels The input frequency is applied to the Threshold Detector input (Pin 11). As discussed in the V/F circuit section of this data sheet, the threshold of pin 11 is approximately (VDD + VSS) /2 ±400mV. Pin 11's input voltage range extends from VDD to about 2.5 V below the threshold. If the voltage on pin 11 goes more than 2.5 volts below the threshold, the V/F mode startup comparator will turn on and corrupt the output voltage. The Threshold Detector input has about 200 mV of hysteresis. In ±5 V applications, the input voltage levels for the TC9400 are ±400mV, minimum. If the frequency source being measured is unipolar, such as TTL or CMOS operat- ing from a +5V source, then an AC coupled level shifter should be used. One such circuit is shown in Figure 6a. The level shifter circuit in Figure 6b can be used in single supply F/V applications. The resistor divider ensures that the input threshold will track the supply voltages. The diode clamp prevents the input from going far enough in the negative direction to turn on the startup comparator. The diode's forward voltage decreases by 2.1 mV/ °C, so for high ambient temperature operation two diodes in series are recommended. VOLTAGE-TO-FREQUENCY/ FREQUENCY-TO-VOLTAGE CONVERTERS TC9400 TC9401 TC9402 |
类似零件编号 - TC9401 |
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类似说明 - TC9401 |
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