4-1/2 DIGIT ANALOG-TO-DIGITAL
CONVERTER WITH ON-CHIP LCD DRIVERS
1
2
3
4
5
6
7
8
TC7129
+
+
V
V
24
24
EXTERNAL
LOGIC
EXTERNAL
LOGIC
TC7129
36
TC7129
DGND
–
+
36
I
LOGIC
DGND
I
LOGIC
23
23
–
–
V
V
Figure 5. External Logic Referenced Directly to DGND
Figure 6. External Logic Referenced to DGND With Buffer
Temperature Compensation
adjusted to give temperature compensation of about 10
mV/°C between V+ (pin 24) and VDISP. The diode between
DGND and VDISP should have a low turn-ON voltage be-
cause VDISP cannot exceed 0.3V below DGND.
For most applications, VDISP (pin 19) can be connected
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
+
+
V
V
1N4148
39 kΩ
39 kΩ
24
24
200 kΩ
20 kΩ
2N2222
TC7129
–
TC7129
19
19
36
V
DISP
V
+
DISP
5 kΩ
36
DGND
DGND
75 kΩ
18 kΩ
23
23
–
–
V
V
Figure 7. Temperature Compensating Circuits
TELCOM SEMICONDUCTOR, INC.
3-239
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
