TC9402 TELCOM [TelCom Semiconductor, Inc], TC9402 Datasheet - Page 5

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

VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGE CONVERTERS
VOLTAGE-TO-FREQUENCY (V/F)
CIRCUIT DESCRIPTION
of charge balancing. The operation of the TC9400 is easily
understood by referring to Figure 1. The input voltage (V
is converted to a current (I
current is then converted to a charge on the integrating
capacitor and shows up as a linearly decreasing voltage at
the output of the op amp. The lower limit of the output
swing is set by the threshold detector, which causes the
reference voltage to be applied to the reference capacitor
for a time period long enough to charge the capacitor to
the reference voltage. This action reduces the charge on
the integrating capacitor by a fixed amount (q = C
V
amount.
REF
The TC9400 V/F converter operates on the principal
), causing the op amp output to step up a finite
TELCOM SEMICONDUCTOR, INC.
INPUT
V IN
0V –10V
50k
OFFSET
ADJUST
820pF
1M
C INT
R IN
+5V
–5V
510k
C REF
180pF
IN
) by the input resistor. This
11
12
10k
5
3
2
I IN
ZERO
ADJUST
AMP OUT
THRESHOLD
DETECT
V REF OUT
–3V
12pF
Figure 1.
R BIAS
100k
START
SELF-
20k
–
+
OpAmp
THRESHOLD
I BIAS
DETECTOR
10 Hz to 10 kHz V/F Converter
REF
60pF
1
IN
)
This dissipates the charge stored on the reference capaci-
tor, so that when the output again crosses zero the system
is ready to recycle. In this manner, the continued discharg-
ing of the integrating capacitor by the input is balanced out
by fixed charges from the reference voltage. As the input
voltage is increased, the number of reference pulses re-
quired to maintain balance increases, which causes the
output frequency to also increase. Since each charge in-
crement is fixed, the increase in frequency with voltage is
linear. In addition, the accuracy of the output pulse width
does not directly affect the linearity of the V/F. The pulse
must simply be long enough for full charge transfer to take
place.
–5V
At the end of the charging period, C
DELAY
3 sec
4
V SS
V DD
+5V
14
(TYPICALLY –5V)
REFERENCE
VOLTAGE
V REF
7
2
TC9400
TC9401
TC9402
GND
6
COMMON
OUTPUT
f OUT /2
f OUT
REF
8
10
9
is shorted out.
+ 5V
+ 5V
TC9400
TC9401
TC9402
R L
10k
R L
10k
3-291
1
2
3
4
5
6
7
8