TC7106 Microchip, TC7106 Datasheet - Page 15

• Manufacturer Part Number: TC7106
• Description: 3-1/2 Digit Analog-to-Digital Converters
• Manufacturer: Microchip

FIGURE 8-2:
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 15Ω 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 Refer-
ence discussion.
8.4
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 500Ω 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
The analog common voltage temperature stability has
been significantly improved (Figure 8-3). The “A” ver-
sion 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.
©
2002 Microchip Technology Inc.
TEST (Pin 37)
Internal Voltage Reference
V+
Source
Power
V-
COMMON MODE VOLTAGE REMOVED IN BATTERY OPERATION WITH
V
GND
IN
-
V+
V-
Measured
= ANALOG COMMON
System
GND
V
Analog
Common
V
V
IN
IN
BUF
+
-
V
REF
TC7106A
C
AZ
-
FIGURE 8-3:
FIGURE 8-4:
V
TC7106/A/TC7107/A
REF
V
INT
+
180
160
140
120
100
200
80
60
40
20
V+
0
Set V
+
Segment
9V
Drive
No Maximum Specified
REF
POL
V-
Maximum
7106A
Typical
OSC1
OSC3
OSC2
TC7106A
TC7107A
V-
Limit
TC
= 1/2 V
BP
Common
ANALOG COMMON
TEMPERATURE
COEFFICIENT
INTERNAL VOLTAGE
REFERENCE
CONNECTION
Analog
V
FULL SCALE
LCD Display
V
REF
REF
Maximum
Specified
ICL7106
V+
Typical
+
1
-
No
36
35
32
V
REF
DS21455B-page 15
Maximum
Specified
ICL7136
Typical
No
24kΩ
1kΩ