11

TC811

TC811-7 11/5/96

© 2001 Microchip Technology Inc.

DS21472A

3-1/2 Digit Analog-To-Digital Converter with

Hold and Differential Reference Inputs

Liquid Crystal Display Sources

Several LCD manufactures supply standard LCD dis-

plays to interface with the TC811 3-1/2 digit analog-to-digital

converter.

Figure 10. TC811 Internal Voltage Reference Connection

Figure 11. Low Parts Count Ratio Metric Resistance Measurement

Representative

Manufacturer

Address/Phone

Crystaloid

5282 Hudson Dr.,

C5335, H5535,

Electronics

Hudson, OH 44236

T5135, SX440

216-655-2429

AND

770 Airport Blvd.,

FE 0801,

Burlingame, CA 94010

FE 0203

415-347-9916

EPSON

3415 Kashikawa St.,

LD-B709BZ

Torrence, CA 90505

LD-H7992AZ

212-534-0360

Hamlin, Inc.

612 E. Lake St.,

3902, 3933, 3903

Lake Mills, WI 53551

414-648-2361

+

–

+

–

ANALOG

COMMON

TC811

LCD

V

+

HLDR

V

–

ANALOG

COMMON

TC811

VREF

+

32

33

36

26

240k

Ω

10k

Ω

VREF

–

VREF

38

+

9V

SET VREF = 1/2 VFULL SCALE

V

+

Oscillator Crystal Source

Representative

Manufacturer

Address/Phone

Part Numbers

STATEK

512 N-Main

CX-1V 40.0

Orange, CA 92668

714-639-7810

Ratiometric Resistance Measurements

The TC811 true differential input and differential refer-

ence make ratiometric readings possible. In ratiometric

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 is passed through the pair (Figure

11). 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

standard, the input voltage will equal the reference voltage

and the display will read 1000. The displayed reading can be

determined from the following expression:

Displayed reading =

x 1000