HD66740 Datasheet, PDF (45/95 Pages) Hitachi Semiconductor – 112 x 80-dot Graphics LCD Controller/Driver

HD66740
Liquid Crystal Display Voltage Generator
When External Power Supply and Internal Operational Amplifiers are Used
To supply LCD drive voltage directly from the external power supply without using the internal booster,
circuits should be connected as shown in figure 22. Here, contrast can be adjusted by software through
the CT bits of the contrast adjustment register.
The HD66740 incorporates a voltage-follower operational amplifier for each V1 to V5 to reduce current
flowing through the internal bleeder-resistors, which generate different levels of liquid-crystal drive
voltages. Thus, potential differences between V_LCD and V1 and between V5 and GND must be 0.4 V or
higher. Note that the OPOFF pin must be grounded when using the operational amplifiers. Place a
capacitor of about 0.1 µF to 0.5 µF between each internal operational amplifier V1OUT to V5OUT
output and GND and stabilize the output level of the operational amplifier.
OPOFF = GND
VLCD
VLCD
VR
V1OUT
R
V2OUT
R0
GND
V3OUT
R
0.1 µF
to 0.5 µF
V4OUT
R
V5OUT
+++++
R
GND
HD66740
+
-
V1
+
-
V2
LCD
driver
+
-
V3
+
-
V4
+
-
V5
GND
Vci
C1+
C1-
C2+
C2-
C3+
C3-
C4+
C4-
VLOUT
Booster
SEG1 to SEG112
COM1 to COM80
Figure 22 External Power Supply Circuit for LCD Drive Voltage Generation
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