tc7136a Microchip Technology Inc., tc7136a Datasheet - Page 15

• Manufacturer Part Number: tc7136a
• Description: Low Power 3-1/2 Digit Analog-to-digital Converter
• Manufacturer: Microchip Technology Inc.

8.0
8.1
Several manufacturers supply standard LCDs to inter-
face with the TC7136A 3-1/2 digit analog-to-digital
converter.
8.2
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
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.

Crystaloid
Electronics
AND
VGI, Inc.
Hamlin, Inc.
2002 Microchip Technology Inc.
Note:
Manufac.
TYPICAL APPLICATIONS
Liquid Crystal Display Sources
Decimal Point and Annunciator
Drive
Ratiometric Resistance
Measurements
Contact LCD manufacturer for full product listing/
specifications.
5282 Hudson Dr.
Hudson, OH 44236
216-655-2429
720 Palomar Ave.
Sunnyvale, CA 94086
408-523-8200
1800 Vernon St. Ste.2,
Roseville,
CA 95678
916-783-7878
612 E. Lake St.
Lake Mills,
WI 53551
414-648-236100
Address/Phone
C5335, H5535,
T5135, SX440
FE 0201, 0501
FE 0203, 0701
FE 2201
I1048, I1126
3902, 3933, 3903
Representative
Part Numbers*
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:
FIGURE 8-1:
TC7136A
TC7136A
Simple Inverter for Fixed Decimal Point
TC7136
TC7136
Displayed(Reading) =
TEST
V+
V+
TEST
TC7136/TC7136A
Multiple Decimal Point or
R
or Display Annunciator
BP
BP
UNKNOWN
Annunciator Driver
21
37
Decimal
Select
Point
≥ 2 x R
DECIMAL POINT AND
ANNUNCIATOR DRIVES
R
R
STANDARD
4049
4030
UNKNOWN
STANDARD
GND
GND
V+
V+
DS21461B-page 15
To LCD Backplane
To LCD
Decimal Point
To LCD
Decimal Point
x 1000