4-1/2 DIGIT ANALOG-TO-DIGITAL
CONVERTER WITH ON-CHIP LCD DRIVERS
1
TC7129
V+
V+
2
24
EXTERNAL
LOGIC
ILOGIC
TC7129
36
DGND
23
V–
Figure 5. External Logic Referenced Directly to DGND
24
EXTERNAL
LOGIC
TC7129
3
36 DGND
ILOGIC
23
V–
Figure 6. External Logic Referenced to DGND With Buffer
4
Temperature Compensation
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
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.
5
V+
V+
1N4148
5 kΩ
75 kΩ
39 kΩ
24
200 kΩ
–
TC7129
19
+
VDISP
36
DGND
23
39 kΩ
24
20 kΩ
2N2222
TC7129
19
VDISP
18 kΩ
36
DGND
23
V–
V–
Figure 7. Temperature Compensating Circuits
TELCOM SEMICONDUCTOR, INC.
6
7
8
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