TC7136ACPL datasheet(12/12 Pages) TELCOM

12 / 12 page

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TELCOM SEMICONDUCTOR, INC.

TC7136

TC7136A

LOW POWER, 3-1/2 DIGIT

ANALOG-TO-DIGITAL CONVERTERS

Figure 11. Decimal Point and Annunciator Drives

Figure 13. Temperature Sensor

Figure 12. Low Parts Count Ratiometric Resistance

Measurement

TC7136

TC7136A

–

VIN

–

VIN

VREF

–

COMMON

5.6 k

Ω

160 k

Ω

20 k

Ω

1N4148

20 k

Ω

0.7%/°C

PTC

TC7136

TC7136A

–

VIN

–

VIN

VREF

–

COMMON

50 k

Ω

160 k

Ω

300 k

Ω

300 k

Ω

50 k

Ω

1N4148

SENSOR

Ratiometric Resistance Measurements

The TC7136A's true differential input and differential

reference 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 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 refer-

ence input. If the unknown equals the standard, the display

will read 1000. The displayed reading can be determined

from the following expression:

Displayed reading =

× 1000.

The display will overrange for RUNKNOWN ≥

×RSTANDARD.

RUNKNOWN

RSTANDARD

VREF

–

VIN

–

ANALOG

COMMON

TC7136

TC7136A

LCD

RSTANDARD

RUNKNOWN

V+

TC7136

TC7136A

V+

TC7136

TC7136A

4049

4030

TEST

GND

TO LCD

DECIMAL

POINT

TO LCD

BLACK

PLANE

TO LCD

DECIMAL

POINTS

DECIMAL

POINT

SELECT

Multiple Decimal Point or

Annunciator Driver

Simple Inverter for Fixed Decimal Point

or Display Annunciator

Figure 14. Positive Temperature Coefficient Resistor

Temperature Sensor

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