TC820 TelCom Semiconductor, TC820 Datasheet - Page 16

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

to power the TC820, when used with a voltage doubler, as
shown in Figure 13. The voltage doubler uses the TC7660
and two external capacitors. With this configuration mea-
surements can be referenced either to Analog Common or
to battery ground.
TC820
3-164
V
age. In the 40-pin package, V
DGND, providing a typical LCD drive voltage of 5 V
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.
APPLICATIONS INFORMATION
Power Supplies
supply such as a 9V battery (Figure 12). The converter will
operate over a range of 7V to 15V. For battery operation,
analog common (COM) provides a common-mode bias
voltage (see analog common discussion in the theory of
operation section). However, measurements cannot be
referenced to battery ground. To do so will exceed the
negative common-mode voltage limit.
DISP
A battery with voltage between 3.5V and 7V can be used
The V
The TC820 is designed to operate from a single power
+
–
Figure 12. Powering the TC820 From a Single 9V Battery
9V
DISP
input sets the peak-to-peak LCD drive volt-
V
V
DD
SS
V
V
COM
REF
+
REF
V
V
–
IN
IN
+
–
DISP
is connected internally to
DISP
TC820
input for applica-
P-P
V
IN
. The
+
–
Digital Ground (DGND)
(Figure 14). The voltage between V
internal supply voltage for the digital section of the TC820.
DGND will sink a minimum of 3mA.
TC820 mode select inputs, and for the frequency and logic
probe inputs. The DGND pin can be used as the negative
supply for external logic gates, such as the logic probe
buffers. To ensure correct counter operation at high fre-
quency, connect a 1 F capacitor from DGND to V
TC820 40-pin package internally connects the LCD V
pin to DGND, and provides an LCD drive voltage of about
5V
DGND will provide a 5V LCD drive voltage.
Digital Input Logic Levels
to V
and the low logic level is DGND +1.5V. In most cases,
digital inputs will be connected directly to V
mechanical switch. CMOS gates can also be used to
control the logic inputs, as shown in the logic probe inputs
section.
+
P-P
Figure 13. Powering the TC820 From a Low-Voltage Battery
Digital ground is generated from an internal zener diode
DGND establishes the low logic level reference for the
DGND also provides the drive voltage for the LCD. The
Logic levels for the TC820 digital inputs are referenced
DD
. In the 44-pin package, connecting the V
3.5V to 6V
+
10 F
and DGND. The high-level threshold is V
2
4
TC7660
3-3/4 A/D CONVERTER WITH
8
3
FREQUENCY COUNTER
TELCOM SEMICONDUCTOR, INC.
10 F
5
+
TC820
AND LOGIC PROBE
V
V
SS
DD
COM
V
V
REF
REF
V
V
+
–
DD
IN
IN
+
–
and DGND is the
DISP
DD
DD
DD
– 1.5V
with a
TC04
pin to
V
.
IN
DISP
+
–