TC7136ACPI datasheet(15/22 Pages) MICROCHIP

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DS21461B-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 ≥ 2xRSTANDARD

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

TEST

GND

To LCD

Decimal Point

To LCD Backplane

To LCD

Decimal Point

Decimal

Point

Select

Multiple Decimal Point or

Annunciator Driver

Simple Inverter for Fixed Decimal Point

or Display Annunciator

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