TC7126/A
DS21458D-page 16 2002-2012 Microchip Technology Inc.
8.0 TYPICAL APPLICATIONS
8.1 Liquid Crystal Display Sources
Several manufacturers supply standard LCDs to inter-
face with the TC7126A, 3-1/2 digit analog-to-digital
converter.
Note: Contact LCD manufacturer for full product list-
ing/specifications.
8.2 Decimal Point and Annunciator
Drive
The TEST pin is connected to the internally generated
digital logic supply ground through a 500resistor. The
TEST pin may be used as the negative supply for exter-
nal CMOS gate segment drivers. LCD annunciators for
decimal points, low battery indication, or function indi-
cation may be added, without adding an additional sup-
ply. No more than 1mA should be supplied by the TEST
pin; its potential is approximately 5V below V+ (see
Figure ).
FIGURE 8-1: Decimal Point and
Annunciator Drives
8.3 Flat Package
The TC7126 is available in an epoxy 64-pin formed
lead package. A test socket for the TC7126ACBQ
device is available:
Part Number: IC 51-42
Manufacturer: Yamaichi
Distribution: Nepenthe Distribution
2471 East Bayshore, Ste. 520
Palo Alto, CA 94043
(650) 856-9332
8.4 Ratiometric Resistance
Measurements
The TC7126A’s true differential input and differential
reference make ratiometric reading possible. In a ratio-
metric operation, an unknown resistance is measured
with respect to a known standard resistance. No
accurately defined reference voltage is needed.
The unknown resistance is put in series with a known
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 determined from the following
expression:
EQUATION 8-1:
Manufacturer Address/Phone
Representative
Part Numbers*
Crystaloid
Electronics
5282 Hudson Dr.
Hudson, OH 44236
216-655-2429
C5335, H5535,
T5135, SX440
AND 720 Palomar Ave.
Sunnyvale, CA 94086
408-523-8200
FE 0801
FE 0203
VGI, Inc. 1800 Vernon St., Ste. 2
Roseville, CA 95678
916-783-7878
LD-B709BZ
LD-H7992AZ
Hamlin, Inc. 612 E. Lake St.
Lake Mills,
WI 53551
414-648-2361
3902, 3933,
3903
TC7126A
V+
V+
TEST
GND
4030
BP
TC7126A
BP
TEST
37
21
V+
V+
GND
To LCD
Decimal
Point
To LCD
Decimal
Point
To LCD
Decimal
Point
To
Backplane
4049
Multiple Decimal Point or
Annunciator Driver
Simple Inverter for Fixed Decimal Point
or Display Annunciator
Displayed (Reading) =
R
UNKNOWN
R
STANDARD
x 1000
