TC9401CPD データシートの表示（PDF） - TelCom Semiconductor Inc => Microchip

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TC9401CPD

VOLTAGE-TO-FREQUENCY/FREQUENCY-TO-VOLTAGE CONVERTERS

TelCom Semiconductor Inc => Microchip 

TC9400

TC9401

TC9402

VOLTAGE-TO-FREQUENCY/

FREQUENCY-TO-VOLTAGE CONVERTERS

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 100µF 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.

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.

+5V

14

VDD

+8V to +5V

14

VDD

10k

Frequency

Input

+5V

0V

3-296

33k 0.01µF

TC9400

11 DET

IN914 1.0M

GND VSS

6

4

Frequency

Input

+5V

0V

–5V

33k 0.01µF

IN914

TC9400

11 DET

1.0M

0.1µF 10k

VSS

4

(A) ±5V Supply

Figure 6. Frequency Input Level Shifter

(B) Single Supply

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