TC9402 TELCOM [TelCom Semiconductor, Inc], TC9402 Datasheet - Page 10

• Manufacturer Part Number: TC9402
• Description: VOLTAGE-TO-FREQUENCY/FREQUENCY-TO-VOLTAGE CONVERTERS
• Manufacturer: TELCOM [TelCom Semiconductor, Inc]

TC9400
TC9401
TC9402
3-296
FREQUENCY-TO-VOLTAGE (F/V)
CIRCUIT DESCRIPTION
an output voltage linearly proportional to the input frequency
waveform.
causes a precise amount of charge (q = C
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 (C
across R
is linearly proportional to the input frequency.
F/V CONVERTER DESIGN INFORMATION
Input/Output Relationships
by the transfer equation:
C
to C
to 100 F are perfectly acceptable for low frequencies.
V
pin 2.
REF
INT
When used as an F/V converter, the TC9400 generates
Each zero crossing at the threshold detector's input
The output voltage is related to the input frequency (f
V
The response time to a change in f
C
When the TC9400 is used in the single-supply mode,
INT
Frequency
Input
). The amount of ripple on V
is defined as the voltage difference between pin 7 and
OUT
INT
and the input frequency.
INT
can be increased to lower the ripple. Values of 1 F
= [V
+5V
0V
averages these pulses into a DC voltage which
REF
C
REF
33k
(A) 5V Supply
R
INT
0.01 F
] f
IN
OUT
.
IN914
is inversely proportional
IN
1.0M
REF
is equal to (R
11
Figure 6.
GND
DET
V
6
REF
TC9400
+5V
V DD
–5V
) to be
V SS
Frequency Input Level Shifter
14
4
INT
INT
IN
FREQUENCY-TO-VOLTAGE CONVERTERS
)
)
Frequency
Input
Input Voltage Levels
input (Pin 11). As discussed in the V/F circuit section of this
data sheet, the threshold of pin 11 is approximately (V
V
V
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.
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.
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.
SS
DD
) /2 400mV. Pin 11's input voltage range extends from
The input frequency is applied to the Threshold Detector
In 5 V applications, the input voltage levels for the
The level shifter circuit in Figure 6b can be used in single
to about 2.5 V below the threshold. If the voltage on pin
+5V
0V
33k
VOLTAGE-TO-FREQUENCY/
0.01 F
(B) Single Supply
TELCOM SEMICONDUCTOR, INC.
0.1 F
IN914
10k
10k
1.0M
11
DET
+8V to +5V
TC9400
V DD
V SS
14
4
DD
+