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TC7107ACKW

3-1/2 Digit Analog-to-Digital Converters

Microchip Technology 

TC7106/A/TC7107/A

10.0 TYPICAL APPLICATIONS

10.1 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

external CMOS gate segment drivers. LCD display

annunciators for decimal points, low battery indication,

or function indication may be added without adding an

additional supply. No more than 1 mA should be

supplied by the TEST pin; its potential is approximately

5V below V+ (see Figure 10-1).

V+

TC7106A

BP 21

TEST 37

V+

4049

GND

To LCD

Decimal

Point

To LCD

Backplane

V+ BP

TC7106A

Decimal

Point

Select

TEST

V+

To LCD

Decimal

Point

4030

GND

FIGURE 10-1:

Decimal Point Drive Using

Test as Logic Ground.

10.2 Ratiometric Resistance

Measurements

The true differential input and differential reference

make ratiometric reading possible. Typically in a

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 is

applied to the reference input. If the unknown equals

the standard, the display will read 1000.

The displayed reading can be determined from the

following expression:

EQUATION 10-1:

Displayed (Reading) = -R----U---N----K---N----O----W----N-- × 1000

RSTANDARD

The display will over range for:

RUNKNOWN ≥ 2 x RSTANDARD

RSTANDARD

RUNKNOWN

VREF + V+

VREF -

VIN +

TC7106A

VIN -

Analog

Common

LCD Display

FIGURE 10-2:

Low Parts Count

Ratiometric Resistance Measurement.

+ 9V

160 kΩ

1N4148

Sensor

R2

50 kΩ

300 kΩ 300kΩ

V+

V-

VIN-

R1

50 kΩ

VIN+ TC7106A

VREF+ VFS = 2V

VREF-

Common

FIGURE 10-3:

Temperature Sensor.

DS21455D-page 20

© 2008 Microchip Technology Inc.

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