VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGE CONVERTERS
TC9400
TC9401
TC9402
C
REF
The exact value is not critical and may be used to trim the
full-scale frequency (see "Input/Output Relationships"). Glass
film or air trimmer capacitors are recommended because of
their stability and low leakage. Locate as close as possible
to pins 5 and 3.
V
DD
, V
SS
Power supplies of
±5V
are recommended. For high-
accuracy requirements, 0.05% line and load regulation and
0.1µF disc decoupling capacitors located near the pins are
recommended.
Improved Single Supply V/F Converter
Operation
A TC9400 which operates from a single 12 to 15V
variable power source is shown in Figure 5. This circuit uses
two Zener diodes to set stable biasing levels for the TC9400.
The Zener diodes also provide the reference voltage, so the
output impedance and temperature coefficient of the Zeners
will directly affect power supply rejection and temperature
performance.
Full scale adjustment is accomplished by trimming the
input current. Trimming the reference voltage is not recom-
mended for high accuracy applications unless an op amp is
used as a buffer, because the TC9400 requires a low
impedance reference (see the V
REF
pin description section
for more information).
The circuit of Figure 5 will directly interface with CMOS
logic operating at 12V to 15V. TTL or 5V CMOS logic can be
accommodated by connecting the output pullup resistors to
the +5V supply. An optoisolator can also be used if an
isolated output is required.
Adjustment Procedure
Figure 1 shows a circuit for trimming the zero location.
Full scale may be trimmed by adjusting R
IN
, V
REF
, or C
REF
.
Recommended procedure for a 10kHz full-scale frequency
is as follows:
(1) Set V
IN
to 10 mV and trim the zero adjust circuit to
obtain a 10Hz output frequency.
(2) Set V
IN
to 10V and trim either R
IN
, V
REF
, or C
REF
to
obtain a 10kHz output frequency.
If adjustments are performed in this order, there should be
no interaction and they should not have to be repeated.
500
VDD = +5V
VSS = – 5V
RIN = 1MΩ
VIN = +10V
TA = +25°C
1 kHz
200
400
CREF (pF) +12pF
300
100
100kHz
0
–1
–2
–3
–4
VREF (V)
–5
–6
–7
Figure 3.
Recommended C
REF
vs V
REF
3-294
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
