hd66740 Renesas Electronics Corporation., hd66740 Datasheet - Page 49

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

Countermeasures for Screen Quality when Using On-chip Operational Amplifier
The HD66740 is an on-chip LCD driver that has an LCD power supply for high duty. Screen quality is
affected by the load current of the high-duty LCD panel used. When the bias (1/10 bias, 1/9.5 bias, 1/9
bias, etc.) is high and the displayed pattern is completely or almost completely white, the white sections
may appear dark.
If this happens, execute the following countermeasures to improve screen quality.
(1) After the change in the V4OUT/V3OUT level is verified, insert about 1 M
(2) Decrease the drive bias and use the new bias level after verifying that the potential differences
Note:
GND or VLCD and V3OUT and then adjust the screen quality (see the following figures). By
inserting resistance, the current consumption increases as much as the boosting factor of the
resistance current. Adjust the resistance after checking the screen quality and the increase in current
consumption.
between V4OUT and GND or VLCD and V3OUT are sufficient.
The actual LCD drive voltage-VLCD used must not exceed 15.0 V, and the absolute rating must
not exceed 16.0 V.
Figure 24-b
Figure 24-c
Vbn
Vbp
VLCD
VLCD
GND
GND
Countermeasure for V3OUT Output
Countermeasure for V4OUT Output
Driver
Driver
Fixed
current
source
Fixed
current
source
49
C
C
V4OUT
V3OUT
RV4
RV3
between V4OUT and
HD66740