2005 Microchip Technology Inc.
DS21461C-page 15
TC7136/TC7136A
8.0
TYPICAL APPLICATIONS
8.1
Liquid Crystal Display Sources
Several manufacturers supply standard LCDs to inter-
face with the TC7136A 3-1/2 digit analog-to-digital
converter.
Note:
Contact LCD manufacturer for full product listing/
specifications.
8.2
Decimal Point and Annunciator
Drive
The TEST pin is connected to the internally generated
digital logic supply ground through a 500
Ω resistor. 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+.
8.3
Ratiometric Resistance
Measurements
The TC7136A's true differential input and differential
reference make ratiometric readings possible. In 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 applied
to the reference input. If the unknown equals the stan-
dard, the display will read 1000. The displayed reading
can be determined from the following expression:
EQUATION 8-1:
The display will over range for:
RUNKNOWN ≥ 2 x RSTANDARD
FIGURE 8-1:
DECIMAL POINT AND
ANNUNCIATOR DRIVES
Manufac.
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 0201, 0501
FE 0203, 0701
FE 2201
VGI, Inc.
1800 Vernon St. Ste.2,
Roseville,
CA 95678
916-783-7878
I1048, I1126
Hamlin, Inc.
612 E. Lake St.
Lake Mills,
WI 53551
414-648-236100
3902, 3933, 3903
Displayed(Reading) =
RUNKNOWN
RSTANDARD
x 1000
V+
TC7136
TC7136A
V+
TC7136
TC7136A
4049
4030
BP
TEST
BP
TEST
GND
To LCD
Decimal Point
To LCD Backplane
To LCD
Decimal Point
Decimal
Point
Select
21
37
Multiple Decimal Point or
Annunciator Driver
Simple Inverter for Fixed Decimal Point
or Display Annunciator