hd66740 Renesas Electronics Corporation., hd66740 Datasheet - Page 45

• Manufacturer Part Number: hd66740
• Description: 112 X 80-dot Graphics Lcd Controller/driver - Hitachi Semiconductor
• Manufacturer: Renesas Electronics Corporation.

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
higher. Note that the OPOFF pin must be grounded when using the operational amplifiers. Place a
capacitor of about 0.1 µ F to 0.5 µ F between each internal operational amplifier V1OUT to V5OUT
output and GND and stabilize the output level of the operational amplifier.
GND
V
LCD
Figure 22
0.1 F
to 0.5 F
+
+
External Power Supply Circuit for LCD Drive Voltage Generation
+
+
VLOUT
+
C3+
C3-
C4+
C4-
Vci
C1+
C1-
C2+
C2-
V1OUT
V2OUT
V3OUT
V4OUT
V5OUT
V
GND
LCD
VR
R
R
R
R
R
0
OPOFF = GND
LCD
Booster
45
and V1 and between V5 and GND must be 0.4 V or
+
+
+
+
+
-
-
-
-
-
HD66740
V1
V2
V3
V4
V5
GND
driver
LCD
SEG1 to SEG112
COM1 to COM80
HD66740