3-239

TELCOM SEMICONDUCTOR, INC.

7

6

5

4

3

1

2

8

Figure 5. External Logic Referenced Directly to DGND

Figure 6. External Logic Referenced to DGND With Buffer

Temperature Compensation

directly to DGND (pin 36). For applications with a wide

temperature range, some LCDs require that the drive levels

vary with temperature to maintain good viewing angle and

display contrast. Figure 7 shows two circuits that can be

adjusted to give temperature compensation of about 10

mV/

EXTERNAL

LOGIC

DGND

V

+

36

24

23

ILOGIC

TC7129

V –

–

+

EXTERNAL

LOGIC

ILOGIC

DGND

23

24

V

+

36

TC7129

V

–

TC7129

1N4148

5 k

Ω

75 k

Ω

200 k

Ω

39 k

Ω

19

36

24

23

V

–

V+

VDISP

DGND

TC7129

2N2222

39 k

Ω

19

36

24

23

V

–

V+

VDISP

DGND

20 k

Ω

18 k

Ω

Figure 7.

Temperature Compensating Circuits

TC7129

4-1/2 DIGIT ANALOG-TO-DIGITAL

CONVERTER WITH ON-CHIP LCD DRIVERS