TC820 TelCom Semiconductor, TC820 Datasheet - Page 15

• 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
in the logic probe mode. In this mode, the DP0/LO and DP1/
HI inputs control the LCD "low" and "high" annunciators
directly. When DP1/HI is connected to V
annunciator will turn on. When DP0/LO is connected to V
the "low" annunciator and the buzzer will turn on. The
internal pull-downs on these pins are disabled when the
logic probe function is selected.
For optimum performance as a logic probe, external level
shifters are recommended. See the applications section for
details.
BUZ IN
Connecting BUZ IN to V
an external pull-down to DGND. BUZ IN can be used with
external circuitry to provide additional functions, such as a
fast, audible continuity indication.
Additional Features
Several additional features are available in the 44-pin pack-
age.
EOC/HOLD
output, this pin goes low for 10 clock cycles at the end of each
conversion. This pulse latches the conversion data into the
display driver section of the TC820.
play. Connecting this pin to V
process. Conversions will continue, but the display will not
change. EOC/HOLD will hold the display reading for either
analog-to-digital or frequency measurements.
shown in Figure 10. The output drive current is only a few
microAmps, so EOC/HOLD can easily be overdriven by an
open-collector logic gate, as well as a FET, bipolar transis-
tor, or mechanical switch. When used as an output, EOC/
HOLD will have a slow rise and fall time due to the limited
output current drive. A CMOS Schmitt trigger buffer is
recommended.
Connecting the LOGIC input to V
These inputs have CMOS logic switching thresholds.
This input controls the TC820 on-chip buzzer driver.
The TC820 is available in 40-pin and 44-pin packages.
EOC/HOLD is a dual-purpose, bidirectional pin. As an
EOC/HOLD can be used to hold (or "freeze") the dis-
The input/output structure of the EOC/HOLD pin is
TELCOM SEMICONDUCTOR, INC.
DD
will turn the buzzer on. There is
DD
inhibits the display update
DD
places the TC820
DD
, the "high"
DD
,
Overrange (OR), Underrange (UR)
is greater than full scale (3999 counts). The UR output will
be high when the display reading is 380 counts or less.
ranging meter function. By logically ANDing these outputs
with the inverted EOC/HOLD output, a single pulse will be
generated each time an underranged or overranged conver-
sion occurs (Figure 11).
V
age. In the 40-pin package, V
DGND, providing a typical LCD drive voltage of 5V
44-pin package includes a separate V
tions requiring a variable or temperature-compensated LCD
drive voltage. See the applications information for sug-
gested circuits.
DISP
TC820
EOC/HOLD
EOC/HOLD
The OR output will be high when the analog input signal
The OR and UR outputs can be used to provide an auto-
The V
Figure 11. Generating Underrange and Overrange Pulses
OR
UR
DISP
Figure 10. EOC/HOLD Pin Schematic
input sets the peak-to-peak LCD drive volt-
4
*
TC820
74HC132
*
500 k
DISP
is connected internally to
DISP
*
*
input for applica-
EOC
DISPLAY
UPDATE
TC820
P-P
. The
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