TC820 TelCom Semiconductor, TC820 Datasheet - Page 10

• Manufacturer Part Number: TC820
• Description: 3-3/4 DIGIT A/D CONVERTER WITH FREQUENCY COUNTER AND LOGIC PROBE
• Manufacturer: TelCom Semiconductor

TC820
3-158
Reference Integrate (Deintegrate) Phase
auto-zero phase, is connected to the input of the integrating
amplifier. The internal sign logic ensures the polarity of the
reference voltage is always connected in the phase opposite
to that of the input voltage. This causes the integrator to
ramp back to zero at a constant rate determined by the
reference potential.
amplifier to reach zero is directly proportional to the ampli-
tude of the voltage that was put on the integrating capacitor
(V
System Timing
the internal decade counters. The four-phase measurement
cycle takes a total of 8000 (4000) counts or 16000 clock
pulses. The 8000 count phase is independent of input signal
magnitude or polarity.
length:
Conversion Phase
1) Auto-Zero:
2) Signal Integrate:
3) Reference Integrate:
4) Integrator Output Zero:
NOTES: 1. This time period is fixed. The integration period for the
Input Overrange
will display "OL" and the "OVERRANGE" LCD annunciator
will be on.
INT
The reference capacitor, which was charged during the
The amount of time required (T
t
The digital reading displayed by the TC820 is:
Digital Count = 2000
The oscillator frequency is divided by 2 prior to clocking
Each phase of the measurement cycle has the following
When the analog input is greater than full scale, the LCD
) during the integration phase:
DEINT
2. Times shown are the RANGE/FREQ at logic low (normal
=
TC820 is:
t
where f
operation). When RANGE/FREQ is logic high, signal
integrate times are 200 counts. See "10:1 Range Change"
section.
INT (TC820)
R
INT
OSC
1,2
V
C
REF
INT
is the clock oscillator frequency.
=
4000
f
V
OSC
INT
V
+
IN
V
= 2000 counts
REF
– V
DEINT
IN
–
) for the integrating
499 to 4499
1 to 4001
Counts
1500
2000
Peak Reading Hold
(or peak) reading. Connecting the PK HOLD input to V
enables the peak hold feature. At the end of each conversion
the contents of the TC820 counter is compared to the
contents of the display register. If the new reading is higher
than the reading being displayed, the higher reading is
transferred to the display register. A "higher" reading is
defined as the reading with the higher absolute value.
reading will not "droop" or slowly decay with time. The held
reading will be retained until a higher reading occurs, the PK
HOLD input is disconnected from V
the TC820 signal integrate period. The TC820 does not
perform transient peak detection of the analog input signal.
However, in many cases, such as measuring temperature or
electric motor starting current, the TC820 "acquisition time"
will not be a limitation. If true peak detection is required, a
simple circuit will suffice. See the applications section for
details.
TC820 is in the frequency counter mode. The counter auto-
ranging feature is disabled when peak reading hold is
selected.
10:1 Range Change
the RANGE/FREQ input. Normally, RANGE/FREQ is held
low by an internal pulldown. Connecting this pin to V
increase the full-scale voltage by a factor of 10. No external
component changes are required.
integrate period. When RANGE/FREQ is connected to V
the signal integration phase of the conversion is reduced by
a factor of 10 (i.e., from 2000 counts to 200 counts).
full scale. This full-scale range will exceed the common-
mode range of the input buffer when operating from a 9V
battery. If range changing is required for the TC820, a higher
supply voltage can be provided or the input voltage can be
divided by 2 externally.
Frequency Counter
the TC820 internal counter can also function as a frequency
counter (Figure 4). In the counter mode, pulses at the
RANGE/FREQ input will be counted and displayed.
clock oscillator. The counter time base is:
The TC820 provides the capability of holding the highest
The peak reading is held in the display register so the
The peak signal to be measured must be present during
The peak reading function is also available when the
The analog input full-scale range can be changed with
The RANGE/FREQ input operates by changing the
In addition to serving as an analog-to-digital converter,
The frequency counter derives its time base from the
t
For the TC820, the 10:1 range change will result in 4V
COUNT
=
40,000
3-3/4 A/D CONVERTER WITH
f
OSC
TELCOM SEMICONDUCTOR, INC.
FREQUENCY COUNTER
AND LOGIC PROBE
DD
, or power is removed.
S
+
will
DD
DD
,