TC7136 View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TC7136 Datasheet PDF : 22 Pages
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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.
Manufac.
Address/Phone
Representative
Part Numbers*
Crystaloid
Electronics
AND
VGI, Inc.
Hamlin, Inc.
5282 Hudson Dr.
Hudson, OH 44236
216-655-2429
C5335, H5535,
T5135, SX440
720 Palomar Ave.
FE 0201, 0501
Sunnyvale, CA 94086 FE 0203, 0701
408-523-8200
FE 2201
1800 Vernon St. Ste.2,
Roseville,
CA 95678
916-783-7878
I1048, I1126
612 E. Lake St.
Lake Mills,
WI 53551
414-648-236100
3902, 3933, 3903
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 500Ω 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.
TC7136/TC7136A
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:
Displayed(Reading) =
RUNKNOWN
RSTANDARD
x 1000
The display will over range for:
RUNKNOWN ≥ 2 x RSTANDARD
FIGURE 8-1:
DECIMAL POINT AND
ANNUNCIATOR DRIVES
Simple Inverter for Fixed Decimal Point
or Display Annunciator
V+
TC7136
TC7136A
21
BP
V+
4049
To LCD
Decimal Point
37
TEST
GND
Multiple Decimal Point or
Annunciator Driver
To LCD Backplane
V+
V+ BP
TC7136
TC7136A
Decimal
Point
Select
To LCD
Decimal Point
TEST
4030
GND
© 2005 Microchip Technology Inc.
DS21461C-page 15
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