TC7117 TelCom, TC7117 Datasheet - Page 8

• Manufacturer Part Number: TC7117
• Description: 3-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTERS WITH HOLD
• Manufacturer: TelCom

TC7116
TC7116A
TC7117
TC7117A
recommended 2V full-scale swing with little loss of accu-
racy. The integrator output can swing within 0.3V of either
supply without loss of linearity.
Analog Common
voltage for battery operation (TC7116/TC7116A) or for any
system where the input signals are floating with respect to
the power supply. The analog common pin sets a voltage
approximately 2.8V more negative than the positive supply.
This is selected to give a minimum end-of-life battery voltage
of about 6V. However, analog common has some attributes
of a reference voltage. When the total supply voltage is large
enough to cause the zener to regulate (>7V), the analog
common voltage will have a low voltage coefficient (0.001%/
%), low output impedance ( 15 ), and a temperature coef-
ficient of less than 20 ppm/ C, typically, and 50 ppm maxi-
mum. The TC7116/TC7117 temperature coefficients are
typically 80 ppm/ C.
shown in Figure 4.
zero and deintegrate. If V
a common-mode voltage exists in the system and is taken
care of by the excellent CMRR of the converter. However, in
some applications, V
(power supply common for instance). In this application,
analog common should be tied to the same point, thus
removing the common-mode voltage from the converter.
The same holds true for the reference voltage; if it can be
conveniently referenced to analog common, it should be.
This removes the common-mode voltage from the reference
system.
FET that can sink 30 mA or more of current to hold the
voltage 3V below the positive supply (when a load is trying
3-210
This pin is included primarily to set the common-mode
An external reference may be used, if necessary, as
Analog common is also used as V
Within the IC, analog common is tied to an N-channel
Figure 4. Using an External Reference
TC7116A
TC7117A
TC7116
TC7117
COMMON
V +
V +
REF
IN
–
will be set at a fixed, known voltage
IN
–
20 k
is different from analog common,
V +
–
IN
1.2V
REF
6.8 k
return during auto-
TC9491CZM
to pull the analog common line positive). However, there is
only 10 A of source current, so analog common may easily
be tied to a more negative voltage, thus overriding the
internal reference.
TEST
TC7117A, it is coupled to the internally-generated digital
supply through a 500
The TEST pin serves two functions. On the TC7117/
OSC
EXT
Figure 6. Exclusive “OR” Gate for Decimal Point Drive
TC7116A
TC7116
TC7116A
3-1/2 DIGIT ANALOG-TO-DIGITAL
Figure 5. Simple Inverter for Fixed Decimal Point
TC7116
TEST
V +
V +
TEST
40
BP
RC NETWORK
BP
CRYSTAL
CONVERTERS WITH HOLD
21
37
TO TEST PIN ON TC7116/TC7116A
TO GROUND PIN ON TC7117/TC7117A
DECIMAL
Figure 7. Clock Circuits
SELECT
POINT
TELCOM SEMICONDUCTOR, INC.
resistor. Thus, it can be used as a
TC7116/TC7116A
TC7117/TC7117A
39
4049
4030
V +
V
GND
GND
+
COUNTER
38
TO LCD
DECIMAL
POINTS
TO LCD
DECIMAL
POINT
TO LCD
BACK-
PLANE
TO