TC7106/A/TC7107/A
DS21455C-page 16
2006 Microchip Technology Inc.
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 measure-
ment 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 20ppm/°C.
This potential can be used to generate the reference
voltage. An external voltage reference will be unneces-
sary in most cases because of the 50ppm/°C maximum
temperature
coefficient.
See
Internal
Voltage
Reference discussion.
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 inter-
nally 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 10mA 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
VBUF
CAZ
VINT
BP
POL
Segment
Drive
OSC1
OSC3
OSC2
V-
V+
VREF+
VREF-
Analog
Common
V-
V+
V-
V+
GND
Measured
System
Power
Source
9V
LCD Display
TC7106A
+
VIN-
VIN+
Typical
No Maximum Specified
No
Maximum
Specified
No
Maximum
Specified
Typical
200
180
160
140
120
100
80
60
40
20
0
Temperature
Coefficient
(ppm/°C)
ICL7136
TC
7106A
ICL7106
Maximum
Limit
V-
Analog
Common
TC7106A
TC7107A
VREF+
32
35
36
24k
Ω
1k
Ω
VREF-
VREF
1
Set VREF = 1/2 VFULL SCALE
V+