TC7107 TelCom, TC7107 Datasheet - Page 16

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

TC7106
TC7106A
TC7107
TC7107A
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: its potential
is approximately 5V below V
3-198
Figure 16. Decimal Point Drive Using TEST as Logic Ground
The TEST pin is connected to the internally-generated
TC7106A
TC7106A
TEST
V +
V +
TEST
BP
BP
21
37
DECIMAL
SELECT
POINT
+
.
4049
4030
V
GND
GND
V +
+
resistor. The
TO LCD
DECIMAL
POINTS
TO LCD
DECIMAL
POINT
TO LCD
BACK-
PLANE
Ratiometric Resistance Measurements
make ratiometric reading possible. Typically in a ratiometric
operation, an unknown resistance is measured with respect
to a known standard resistance. No accurately defined
reference voltage is needed.
standard and a current passed through the pair. The voltage
developed across the unknown is applied to the input and
the voltage across the known resistor is applied to the
reference input. If the unknown equals the standard, the
display will read 1000. The displayed reading can be deter-
mined from the following expression:
standard.
R
UNKNOWN
R
The true differential input and differential reference
The unknown resistance is put in series with a known
Displayed Reading =
The display will overrange for R Unknown
STANDARD
Figure 17. Low Parts Count Ratiometric Resistance
3-1/2 DIGIT A/D CONVERTERS
Measurement
TELCOM SEMICONDUCTOR, INC.
V
V
V
ANALOG
COMMON
V
REF
+
REF
+
IN
IN
–
–
R Unknown
R Standard
TC7106A
V +
x 1000
LCD DISPLAY
2 x R