2008 Microchip Technology Inc.
DS21455D-page 17
TC7106/A/TC7107/A
FIGURE 8-2:
Common Mode Voltage Removed in Battery Operation with VIN- = Analog Common.
The analog common pin serves to set the analog section
reference or common point. The TC7106A is specifically
designed to operate from a battery, or in any
measurement system where input signals are not
referenced (float), with respect to the TC7106A power
source. The analog common potential of V+ – 3.0V gives
a 6V end of battery life voltage. The common potential
has a 0.001% voltage coefficient and a 15
Ω output
impedance.
With sufficiently high total supply voltage (V+ – V- >
7.0V), analog common is a very stable potential with
excellent temperature stability, typically 20 ppm/°C.
This potential can be used to generate the reference
voltage.
An
external
voltage
reference
will
be
unnecessary in most cases because of the 50 ppm/°C
8.4
TEST (Pin 37)
The TEST pin potential is 5V less than V+. TEST may
be used as the negative power supply connection for
external CMOS logic. The TEST pin is tied to the
internally generated negative logic supply (Internal
Logic Ground) through a 500
Ω resistor in the
TC7106A. The TEST pin load should be no more than
1mA.
If TEST is pulled to V+ all segments plus the minus sign
will be activated. Do not operate in this mode for more
than
several
minutes
with
the
TC7106A.
With
TEST = V+, the LCD segments are impressed with a
DC voltage which will destroy the LCD.
The TEST pin will sink about 10 mA when pulled to V+.
8.5
Internal Voltage Reference
The analog common voltage temperature stability has
version of the industry standard circuits allow users to
upgrade old systems and design new systems without
external voltage references. External R and C values
do not need to be changed.
Figure 8-4 shows analog
common supplying the necessary voltage reference for
the TC7106A/TC7107A.
FIGURE 8-3:
Analog Common
Temperature Coefficient.
FIGURE 8-4:
Internal Voltage Reference
Connection.
V
BUF
C
AZ
V
INT
BP
POL
Segment
Drive
OSC1
OSC3
OSC2
V-
V+
V
REF+
V
REF -
Analog
Common
V-
V+
V-
V+
GND
Measured
System
Power
Source
9V
LCD Display
TC7106A
+
V
IN -
V
IN +
Typical
No Maximum Specified
No
Maximum
Specified
No
Maximum
Specified
Typical
200
180
160
140
120
100
80
60
40
20
0
T
e
mp
er
at
u
re
C
o
e
ffi
c
ie
n
t
(p
p
m
/°
C)
ICL7136
TC
7106A
ICL7106
Maximum
Limit
V-
Analog
Common
TC7106A
TC7107A
V
REF +
32
35
36
24k
Ω
1k
Ω
V
REF
-
V
REF
1
Set V
REF
= 1/2 V
FULL SCALE
V+