VOLTAGE-TO-FREQUENCY/
FREQUENCY-TO-VOLTAGE CONVERTERS
TC9400
TC9401
TC9402
3 µsec
TYP
fOUT
fOUT/2
1/f
VREF
AMP
OUT
NOTES:
1. To adjust fMIN, set VIN = 10mV and adjust the 50kΩ offset for 10Hz output.
2. To adjust fMAX, set VIN = 10V and adjust RIN or VREF for 10 kHz output.
3. To increase fOUT MAX to 100kHz, change CREF to 2pF and CINT to 75pF.
4. For high-performance applications, use high-stability components for RIN, CREF, VREF (metal film
resistors and glass capacitors). Also, separate output ground (pin 9) from input ground (pin 6).
0V
CREF
CINT
Figure 2 . Output Waveforms
The TC9400 contains a "self-start" circuit to ensure the
V/F converter always operates properly when power is first
applied. In the event that, during power-on, the Op Amp
output is below the threshold and C
REF
is already charged,
a positive voltage step will not occur. The op-amp output will
continue to decrease until it crosses the –3.0V threshold of
the "self-start" comparator. When this happens, an internal
resistor is connected to the op-amp input, which forces the
output to go positive until the TC9400 is in its normal
operating mode.
The TC9400 utilizes low power CMOS processing for
low input bias and offset currents with very low power
dissipation. The open-drain N-channel output FETs provide
high voltage and high current sink capability.
PIN FUNCTIONS
Threshold Detector Input
In the V/F mode, this input is connected to the amplifier
output (pin 12) and triggers a 3
µsec
pulse when the input
voltage passes through its threshold. In the F/V mode, the
input frequency is applied to this input.
The nominal threshold of the detector is halfway be-
tween the power supplies, or (V
DD
+ V
SS
)/2
±400mV.
The
TC9400's charge balancing V/F technique is not dependent
on a precision comparator threshold, because the threshold
only sets the lower limit of the op-amp output. The op-amp's
peak-to-peak output swing, which determines the frequency,
is only influenced by external capacitors and by V
REF
.
VOLTAGE-TO-TIME MEASUREMENTS
The TC9400 output can be measured in the time do-
main as well as the frequency domain. Some microcom-
puters, for example, have extensive timing capability but
limited counter capability. Also, the response time of a time
domain measurement is only the period between two out-
put pulses, while the frequency measurement must accu-
mulate pulses during the entire counter timebase period.
Time measurements can be made from either the
TC9400's Pulse Freq Out output or from the Freq/2 output.
The Freq/2 output changes state on the rising edge of
Pulse Freq Out, so Freq/2 is a symmetrical square wave at
one half the pulse output frequency. Timing measurements
can therefore be made between successive Pulse Freq
Out pulses, or while Freq/2 is high (or low).
3-292
Pulse Freq Out
This output is an open-drain N-channel FET which
provides a pulse waveform whose frequency is proportional
to the input voltage. This output requires a pull-up resistor
and interfaces directly with MOS, CMOS, and TTL logic.
Freq/2 Out
This output is an open-drain N-channel FET which
provides a square wave one-half the frequency of the pulse
frequency output. The Freq/2 output will change state on the
rising edge of Pulse Freq Out. This output requires a pull-
up resistor and interfaces directly with MOS, CMOS, and
TTL logic.
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
