TC9400/9401/9402
3.2
Voltage-to-Time Measurements
4.0
4.1
PIN FUNCTIONS
Threshold Detector Input
The TC9400 output can be measured in the time
domain as well as the frequency domain. Some micro-
computers, for example, have extensive timing capabil-
ity, but limited counter capability. Also, the response
time of a time domain measurement is only the period
between two output pulses, while the frequency mea-
surement must accumulate pulses during the entire
counter time-base period.
Time measurements can be made from either the
TC9400's PULSE FREQ OUT output, or from the
FREQ/2 OUT output. The FREQ/2 OUT output
changes state on the rising edge of PULSE FREQ
OUT, so FREQ/2 OUT is a symmetrical square wave at
one-half the pulse output frequency. Timing measure-
ments can, therefore, be made between successive
PULSE FREQ OUT pulses, or while FREQ/2 OUT is
high (or low).
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 ±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
.
4.2
Pulse Freq Out
This output is an open drain N-channel FET, which pro-
vides 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).
FIGURE 4-1:
OUTPUT WAVEFORMS
3µsec
Typ.
F
OUT
F
OUT
/2
1/f
C
REF
C
INT
V
REF
Amp Out
0V
Notes:
1. To adjust F
MIN
, set V
IN
= 10mV and adjust the 50kΩ offset for 10Hz output.
2. To adjust F
MAX
, set V
IN
= 10V and adjust R
IN
or V
REF
for 10kHz output.
3. To increase F
OUT
MAX
to 100kHz, change C
REF
to 2pF and C
INT
to 75pF.
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).
©
DS21483B-page 8
2002 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
