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