11

FN3086.6

July 21, 2005

Reference Voltage

The analog input required to generate full scale output (2000

many applications where the A/D is connected to a

transducer, there will exist a scale factor other than unity

between the input voltage and the digital reading. For

instance, in a weighing system, the designer might like to

have a full scale reading when the voltage from the

transducer is 0.662V. Instead of dividing the input down to

200mV, the designer should use the input voltage directly

resistor and capacitor would be 330k

Ω and 0.047µF. This

makes the system slightly quieter and also avoids a divider

network on the input. Another advantage of this system

Temperature and weighing systems with a variable fare are

examples. This offset reading can be conveniently

generated by connecting the voltage transducer between

IN HI and COMMON and the variable (or fixed) offset

voltage between COMMON and IN LO.

Typical Applications

The ICL7136 may be used in a wide variety of

configurations. The circuits which follow show some of the

possibilities, and serve to illustrate the exceptional versatility

of these A/D converters.

The following application notes contain very useful

information on understanding and applying this part and are

available from Intersil.

Application Notes

NOTE #

DESCRIPTION

AN016

“Selecting A/D Converters”

AN017

“The Integrating A/D Converter”

AN018

“Do’s and Don’ts of Applying A/D Converters”

AN023

“Low Cost Digital Panel Meter Designs”

AN032

“Understanding the Auto-Zero and Common Mode

Performance of the ICL7136/7/9 Family”

AN046

“Building a Battery-Operated Auto Ranging DVM with

the ICL7106”

AN052

FIGURE 8. ICL7136 USING THE INTERNAL REFERENCE

FIGURE 9. RECOMMENDED COMPONENT VALUES FOR 2V

FULL SCALE

28

40

39

38

37

36

35

34

33

32

31

30

29

27

26

25

24

23

22

21

OSC 1

OSC 2

OSC 3

TEST

REF HI

REF LO

COMMON

IN HI

IN LO

A-Z

BUFF

INT

V

-

G2

C3

A3

G3

BP

50pF

TO PIN 1

= 100mV

0.1

µF

0.01

µF

1M

Ω

180k

Ω

20k

Ω

240k

Ω

IN

+

-

9V

180k

Ω

0.047

µF

0.47

µF

TO BACKPLANE

TO DISPLAY

Values shown are for 200mV full scale, 3 readings/sec., floating

supply voltage (9V battery).

+

-

28

40

39

38

37

36

35

34

33

32

31

30

29

27

26

25

24

23

22

21

OSC 1

OSC 2

OSC 3

TEST

REF HI

REF LO

COMMON

IN HI

IN LO

A-Z

BUFF

INT

V

-

G2

C3

A3

G3

BP/GND

50pF

TO PIN 1

= 100mV

0.1

µF

0.01

µF

1M

Ω

180k

Ω

250k

Ω 240kΩ

IN

+

-

1.8M

0.047

µF

0.01

µF

TO DISPLAY

V+

V-

ICL7136