
2007 Microchip Technology Inc.
DS21483D-page 7
TC9400/9401/9402
2.6
Pulse Freq Out
This output is an open-drain N-channel FET, which
provides a pulse waveform whose frequency is propor-
tional to the input voltage. This output requires a pull-
up resistor and interfaces directly with MOS, CMOS,
2.7
Output Common
The sources of both the FREQ/2 OUT and the PULSE
FREQ OUT are connected to this pin. An output level
swing from the drain voltage to ground, or to the VSS
supply, may be obtained by connecting this pin to the
appropriate point.
2.8
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 OUT 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.
2.9
Threshold Detector Input
In the V/F mode, this input is connected to the AMPLI-
FIER OUT output (Pin 12) and triggers a 3 s 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 half way
between the power supplies, or (VDD + VSS)/2 ±400
mV. 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 VREF.
2.10
Amplifier Out
This pin is the output stage of the operational amplifier.
During V/F operation, a negative going ramp signal is
available at this pin. In the F/V mode, a voltage
proportional to the frequency input is generated.
FIGURE 2-1:
Output Waveforms.
3ms
Typ.
1/f
FOUT
FOUT/2
Amp Out
VREF
0V
CREF
CINT
Note 1: To adjust FMIN, set VIN = 10 mV and adjust the 50 kΩ offset for 10 Hz output.
2: To adjust FMAX, set VIN = 10V and adjust RIN or VREF for 10 kHz output.
3: To increase FOUTMAX to 100 kHz, change CREF to 2 pF and CINT to 75 pF.
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).