VFC100_00 Datasheet, PDF (5/16 Pages) Texas Instruments – Synchronized VOLTAGE-TO-FREQUENCY CONVERTER

C _INT
5
4
I_IN
V_IN
7
R_IN
Integrator
6 20kΩ
S₁
F_C Clock
TTL/CMOS
14
10
Comparator
Clocked
Logic
1mA
I₁
–V_CC
13
15
Analog
Ground
5V
Reference
16
FIGURE 1. Circuit Diagram for Voltage-to-Frequency Mode.
0.1µF ^+VCC
1
+V_CC
Output
One-Shot
+V_L 0.1µF
11
f_OUT
12
–V_CC
Digital
Ground
9
+V_CC
8 0.1µF
–V_CC
Clock
Integrator 5V
f_O
FIGURE 2. Timing Diagram for Voltage-to-Frequency Mode.
the necessary transitions of the clock). Output pulses are
thus made to align with rising edges of the external clock.
This causes the instantaneous output frequency to be a
subharmonic of the clock frequency. The average frequency,
however, will be an accurate analog of the input voltage.
A full scale input of 10V (or an input current of 0.5mA)
causes a nominal output frequency equal to half the clock
frequency. The transfer function is
f_OUT = (V_IN/20V) f_CLOCK.
Figure 3 shows the transfer function graphically. Note that
inputs above 10V (or 0.5mA) do not cause an increase in the
output frequency. This is an easily detectable indication of
an overrange input. In the overrange condition, the integra-
tor amplifier will ramp to its negative output swing limit.
f_FS = f_CLOCK /2
f _OUT
When the input signal returns to within the linear range, the
integrator amplifier will recover and begin ramping upward
during the reset period.
INSTALLATION AND
OPERATING INSTRUCTIONS
The integrator capacitor C_INT (see Figure 1) affects the
magnitude of the integrator voltage waveform. Its absolute
accuracy is not critical since it does not affect the transfer
function. This allows a wide range of capacitance to produce
excellent results. Figure 4 facilitates choosing an appropriate
10µ
1µ
0.1µ
0.01µ
1000p
Integrator Swing*
+100mV
–75mV
+1V
–0.75V
+2.5V
–1.9V
0
V _IN
10V
0
I _IN
0.5mA
100p
100
1k
10k
100k
1M
10M
Full-Scale Frequency (Hz)
* This is the maximum swing of the integrator output voltage
referred to the comparator noninverting input voltage.
FIGURE 3. Transfer Function for Voltage-to-Frequency Mode. FIGURE 4. Integrator Capacitor Selection Graph.
®
5
VFC100