TC7107 TelCom, TC7107 Datasheet - Page 13

• Manufacturer Part Number: TC7107
• Description: 3-1/2 DIGIT A/D CONVERTERS
• Manufacturer: TelCom

Analog Common (Pin 32)
approximately 3.0V below V
to be between 2.7V and 3.35 V below V
is tied internally to the N channel FET capable of sinking
20mA. This FET will hold the common line at 3.0V should an
external load attempt to pull the common line toward V
Analog common source current is limited to 10 A. Analog
common is therefore easily pulled to a more negative
voltage (i.e., below V
to analog common during the auto-zero cycle. During the
reference-integrate phase, V
mon. If V
a common-mode voltage exists. This is rejected by the
converter's 86dB common-mode rejection ratio. In battery
operation, analog common and V
removing common-mode voltage concerns. In systems where
V
voltage, analog common should be connected to V
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
The common potential has a 0.001%/% voltage coefficient
and a 15
> 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 unnecessary in most
cases because of the 50ppm/ C maximum temperature
coefficient. See Internal Voltage Reference discussion.
Test (Pin 37)
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 resistor in the TC7106A. The TEST pin load should be
no more than 1mA .
will be activated. Do not operate in this mode for more than
several minutes with the TC7106A. With TEST = V
segments are impressed with a DC voltage which will
destroy the LCD.
3-1/2 DIGIT A/D CONVERTERS
IN
–
is connected to the power supply ground or to a given
The analog common pin is set at a voltage potential
The TC7106A connects the internal V
The analog common pin serves to set the analog section
With sufficiently high total supply voltage (V
The TEST pin potential is 5V less than V
If TEST is pulled to V
The TEST pin will sink about 10mA when pulled to V
TELCOM SEMICONDUCTOR, INC.
IN
–
is not externally connected to analog common,
output impedance.
+
– 3.0V gives a 6 V end of battery life voltage.
+
– 3.0V).
+
all segments plus the minus sign
IN
–
+
. The potential is guaranteed
is connected to analog com-
IN
–
are usually connected,
+
. Analog common
IN
+
+
. TEST may be
and V
+
IN
–
the LCD
IN
–
+
inputs
.
– V
+
+
–
.
.
Internal Voltage Reference Stability
been significantly improved (Figure 10). The “A” 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 11 shows analog common supplying the
necessary voltage reference for the TC7106A/TC7107A.
The analog common voltage temperature stability has
Figure 10. Analog Common Temperature Coefficient
200
180
160
140
120
100
80
60
40
20
Figure 11. Internal Voltage Reference Connection
0
V –
NO
MAXIMUM
SPECIFIED
MAXIMUM
SET V REF = 1/2 V FULL SCALE
TYPICAL
TC7106A
TC7107A
7106A
LIMIT
TC
COMMON
ANALOG
V REF
V REF
+
–
V +
NO MAXIMUM
1
SPECIFIED
TYPICAL
ICL7106
36
35
32
V REF
NO MAXIMUM
SPECIFIED
24k
1k
TYPICAL
ICL7136
TC7106A
TC7107A
TC7106
TC7107
3-195
1
2
3
4
5
6
7
8