TC820 TelCom Semiconductor, TC820 Datasheet - Page 11

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

3-3/4 A/D CONVERTER WITH
FREQUENCY COUNTER
AND LOGIC PROBE
when a 40 kHz oscillator is used. The frequency counter
accuracy is determined by the oscillator accuracy. For
accurate frequency measurements, a crystal oscillator is
recommended.
proper range. Auto-range operation extends over four
decades, from 3.999 kHz to 3.999 MHz. Decimal points are
set automatically in the frequency mode (Figure 5).
are CMOS levels. For best counter operation, an external
buffer is recommended. See the applications section for
details.
Logic Probe
(Figure 6). This mode is selected when the LOGIC input is
high. Two dual-purpose pins, which normally control the
decimal points, are used as logic inputs. Connecting either
input to a logic high level will turn on the corresponding LCD
annunciator. When the "low" annunciator is on the buzzer
will be on. As with the frequency counter input, external level
shifters/buffers are recommended for the logic probe inputs.
VOLTS is low (A/D mode), the ADC will remain in the auto-
zero mode. The LCD will read "OL" and all decimal points will
be off (Figure 7).
RANGE/
VOLTS
Thus, the counter will operate with a 1-second time base
The frequency counter will automatically select the
The logic switching levels of the RANGE/FREQ input
The TC820 can also function as a simple logic probe
When the logic probe function is selected while FREQ/
FREQ/
FREQ
TELCOM SEMICONDUCTOR, INC.
A/D CONVERTER/FREQUENCY
FREQUENCY
INPUT
OSCILLATOR
COUNTER SELECT
CLOCK
20,000
PROGRAMMABLE
( 1, 10, 100, 1000)
DIVIDER
2
OF A/D CONVERTER
FROM INTEGRATOR
TC820
FREQUENCY COUNTER
A/D CONVERTER
Figure 4. TC820 Counter Operation
COMPARATOR
POINT DRIVERS
AUTO-RANGE
TO DECIMAL
CONTROL
(counter mode), the frequency counter will continue to
operate. The display will read "OL" but the decimal points will
be visible. If the logic probe input is also connected to the
RANGE/FREQ input, bringing the LOGIC input low will
immediately display the frequency at the logic probe input.
Analog Pin Functional Description
Differential Signal Inputs (V
accepts input signals within the input stage common-mode
voltage (V
+1.5V. Common-mode voltages are removed from the sys-
tem when the TC820 operates from a battery or floating
power source (isolated from measured system) and V
connected to analog common. (See Figure 8.)
If the logic probe is active while FREQ/VOLTS is high
The TC820 is designed with true differential inputs, and
ENABLE
COUNT
LCD DECODER/DRIVERS
3-3/4 DIGIT COUNTER
DATA LATCH, PEAK
HOLD REGISTER,
UNDERRANGE
CM
DETECT
) range. The typical range is V
LCD
OVERFLOW
+
IN
OVERRANGE
), (V
DETECT
IN
–
)
DD
–1V to V
TC820
3-159
SS
SS
is
1
2
3
4
5
6
7
8