TC9400_06 Datasheet, PDF (9/24 Pages) Microchip Technology – Voltage-to-Frequency/Frequency-to-Voltage Converters

TC9400/9401/9402
4.0 PIN FUNCTIONS
4.1 Threshold Detector Input
In the V/F mode, this input is connected to the AMPLI-
FIER OUT output (Pin 12) and triggers a 3μsec 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 (V_DD + V_SS)/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 V_REF.
F_OUT
3msec
Typ.
4.2 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,
and TTL logic (see Figure 4-1).
4.3 Freq/2 Out
This output is an open drain N-channel FET, which pro-
vides 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.
F_OUT/2
1/f
Amp Out
V_REF
0V
C_REF
C_INT
Notes:
1. To adjust F_MIN, set V_IN = 10 mV and adjust the 50 kW offset for 10 Hz output.
2. To adjust F_MAX, set V_IN = 10V and adjust R_IN or V_REF for 10 kHz output.
3. To increase F_OUTMAX to 100 kHz, change C_REF to 2pF and C_INT to 75 pF.
4. For high performance applications, use high stability components for R_IN, C_REF, V_REF (metal film
resistors and glass capacitors). Also, separate output ground (Pin 9) from input ground (Pin 6).
FIGURE 4-1:
Output Waveforms
4.4 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 V_SS
supply, may be obtained by connecting this pin to the
appropriate point.
4.5 R_BIAS
An external resistor, connected to V_SS, sets the bias
point for the TC9400. Specifications for the TC9400 are
based on R_BIAS = 100 kΩ ±10%, unless otherwise
noted.
Increasing the maximum frequency of the TC9400
beyond 100 kHz is limited by the pulse width of the
pulse output (typically 3μsec). Reducing R_BIAS will
decrease the pulse width and increase the maximum
operating frequency, but linearity errors will also
increase. R_BIAS can be reduced to 20 kΩ, which will
typically produce a maximum full scale frequency of
500 kHz.
4.6 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.
4.7 Zero Adjust
This pin is the non-inverting input of the operational
amplifier. The low frequency set point is determined by
adjusting the voltage at this pin.
4.8 I_IN
The inverting input of the operational amplifier and the
summing junction when connected in the V/F mode. An
input current of 10 μA is specified, but an over range
current up to 50 μA can be used without detrimental
effect to the circuit operation. I_IN connects the summing
junction of an operational amplifier. Voltage sources
cannot be attached directly, but must be buffered by
external resistors.
© 2006 Microchip Technology Inc.
DS21483C-page 9