TC811 TelCom Semiconductor, TC811 Datasheet - Page 10

• Manufacturer Part Number: TC811
• Description: 3-1/2 DIGIT A/D CONVERTER WITH HOLD AND DIFFERENTIAL REFERENCE INPUTS
• Manufacturer: TelCom Semiconductor

TC811
Analog Common (Pin 32)
approximately 3.0V below V
to be between 2.70V and 3.35V below V
is tied internally to an N channel FET capable of sinking
100 A. This FET will hold the common line at 3.0V below V
should an external load attempt to pull the common line
toward V
Analog common 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
Common, 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
usually connected, removing common-mode voltage con-
cerns. In systems where V
supply ground or to a given voltage, Analog Common should
be connected to V
section reference or common point. The TC811 is specifi-
cally designed to operate from a battery or in any measure-
ment system where input signals are not referenced (float)
with respect to the TC811 power source. The Analog Com-
mon potential of V
voltage. The analog common potential has a voltage coef-
ficient of 0.001%/%.
7.0V), Analog Common is a very stable potential with
excellent temperature stability (typically 35ppm/ C). This
potential can be used to generate the TC811 reference
voltage. An external voltage reference will be unnecessary
in most cases because of the 35ppm/ C temperature coef-
ficient. See TC811 Internal Voltage Reference discussion.
TEST (Pin 37)
used as the negative power supply connection when inter-
facing the TC811 to external CMOS logic. The TEST pin is
tied to the internally generated negative logic supply through
a 500
1mA. See the applications section for additional information
on using TEST as a negative digital logic supply.
minus sign will be activated. Do not operate in this mode for
more than several minutes, because when TEST is pulled to
V
which may cause damage to the LCD.
3-146
+
, the LCD Segments are impressed with a DC voltage
The Analog Common pin is set at a voltage potential
The TC811 connects the internal V
The Analog Common pin serves to set the analog
With a sufficiently high total supply voltage (V
The TEST pin potential is 5V less the V
If TEST is pulled “HIGH” (V
resistor. The TEST pin may be used to sink up to
+
. Analog common source current is limited to 1 A.
IN
–
IN
is not externally connected to Analog
–
+
+
.
– 3.0V gives a 7V end of battery life
– 3.0V).
IN
+
. This potential is guaranteed
–
IN
–
is connected to the power
+
is connected to Analog
), all segments plus the
IN
+
+
. Analog common
and V
+
. TEST may be
IN
–
inputs to
+
3-1/2 DIGIT A/D CONVERTER WITH HOLD AND
– V
IN
–
are
–
>
+
APPLICATIONS INFORMATION
Decimal Point and Annunciator Drive
digital logic supply ground through a 500
TEST pin may be used as the negative supply for external
CMOS gate segment drivers. LCD display annunciators for
decimal points, low battery indication, or function indication
may be added without adding an additional supply. No more
than 1mA should be supplied by the TEST pin. The TEST pin
potential is approximately 5V below V
Internal Voltage Reference
bility has been significantly improved. This improved device
can be used to upgrade old systems and design new
systems without external voltage references. External R and
C values do not need to be changed, however, noise
performance will be improved by increasing C
Zero Capacitor section). Figure 10 shows Analog Common
supplying the necessary voltage reference for the TC811.
DIFFERENTIAL REFERENCE INPUTS
The TEST pin is connected to the internally generated
The TC811 Analog Common voltage temperature sta-
HDLR
TC811
TC811
TEST
V +
V +
Figure 9. Display Annunciator Drivers
TEST
BP
BP
DECIMAL
TELCOM SEMICONDUCTOR, INC.
SELECT
POINT
4049
4030
+
V +
GND
V +
GND
.
TO "HOLD"
ANNUNCIATOR
resistor. The
TO LCD
DECIMAL
POINT
TO LCD
BACK-
PLANE
AZ
TO LCD
DECIMAL
POINTS
(See Auto