TC820 TelCom Semiconductor, TC820 Datasheet - Page 13

• 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
large common-mode voltages, C
pared to stray node capacitance. A 0.1 F capacitor is
typical.
common temperature coefficient, providing a very stable
voltage suitable for use as a voltage reference. The
temperature coefficient of analog common is typically
35ppm/ C.
To prevent roll-over-type errors from being induced by
The TC820 offers a significantly improved analog
**
*
TELCOM SEMICONDUCTOR, INC.
"HIGH" ANNUNCIATOR WILL BE ON WHEN DP1/HI =
LOGIC HIGH
"LOW" ANNUNCIATOR AND BUZZER WILL BE ON
WHEN DP0/LO = LOGIC HIGH
HIGH
LOW
Figure 7. LCD During Logic Probe Operation
POWER
SOURCE
V
+
*
**
V
–
MEASURED
V
V
Figure 8. Common-Mode Voltage Removed in Battery Operation With V
+
SYSTEM
–
GND
GND
REF
should be large com-
V
V
ANALOG
COMMON
IN
IN
+
–
V
BUF
C
AZ
V
REF
–
V
INT
V
Analog Common
approximately 3.3V below V
to be between 3.15V and 3.45V below V
is tied internally to an N-channel FET capable of sinking
3mA. This FET will hold the common line at 3.3V below V
should an external load attempt to pull the common line
toward V
12 A, and is therefore easily pulled to a more negative
voltage (i.e., below V
analog common during the auto-zero cycle. During the
reference integrate phase, V
common. If V
a common-mode voltage exists. This is rejected by the
converter's 86dB common-mode rejection ratio. In battery-
powered applications, analog common and V
connected, removing common-mode voltage concerns. In
systems where V
or to a given voltage, analog common should be connected
to V
reference or common point. The TC820 is specifically
designed to operate from a battery or in any measurement
REF
+
TC820
IN
The analog common pin is set at a voltage potential
The TC820 connects the internal V
–
The analog common pin serves to set the analog section
SEGMENT
DRIVE
V
.
DD
+
DD
9V
. Analog common source current is limited to
BP1
–
IN
V
SS
is not externally connected to analog common,
OSC1
–
IN
BP2
OSC2
OSC3 NC
is connected to the power supply ground
–
IN
DD
LCD
= Analog Common
BP3
– 3.3V).
DD
. This potential is guaranteed
IN
–
is connected to analog
DD
+
IN
. Analog common
and V
–
IN
are usually
–
IN
TC820
inputs to
3-161
DD
1
2
3
4
5
6
7
8