3-228

TELCOM SEMICONDUCTOR, INC.

3-1/2 DIGIT

ANALOG-TO-DIGITAL CONVERTERS

TC7126

TC7126A

8

14

7

13

12

11

10

9

1

2

3

4

5

6

TC7126A

9V

VIN

9 M

Ω

900 k

Ω

90 k

Ω

10 k

Ω

2V

20V

200V

200 mV

1N4148

10 M

Ω

1 M

Ω

0.02

µF

1 M

Ω 10%

47 k

Ω

1W

10%

20 k

Ω

10%

6.8 µF

1 µF

COM

C1 = 3 pF TO 10 pF, VARIABLE

C2 = 132 pF, VARIABLE

+

+

AD636

2.2

µF

0.01

µF

10 k

Ω

240 k

Ω

SEGMENT

DRIVE

LCD

39

40

28

27

38

29

26

1

35

32

31

30

26

36

BP

V

+

V

–

V

+

REF

V

–

REF

ANALOG

COMMON

V

+

IN

V

+

OUT

V

–

C1

C2

Figure 9. Decimal Point and Annunciator Drives

Figure 11. 3-1/2 Digit True RMS AC DMM

+

–

+

–

ANALOG

COMMON

TC7126A

LCD

V

+

TC7126A

DECIMAL

POINT

SELECT

V

+

V

+

TEST

GND

4030

TO LCD

DECIMAL

POINTS

BP

TC7126A

BP

TEST

37

21

V+

V+

GND

TO LCD

DECIMAL

POINT

TO

BACKPLANE

4049

Multiple Decimal Point or

Annunciator Driver

Simple Inverter for Fixed Decimal Point

or Display Annunciator

Figure 10. Low Parts Count Ratiometric Resistance Measurement