HD66740 Datasheet, PDF (49/95 Pages) Hitachi Semiconductor – 112 x 80-dot Graphics LCD Controller/Driver

HD66740
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 MΩ between V4OUT and
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.
(2) Decrease the drive bias and use the new bias level after verifying that the potential differences
between V4OUT and GND or VLCD and V3OUT are sufficient.
VLCD
Driver
V4OUT
Fixed
Vbn
current
source
C
RV4
GND
Figure 24-b Countermeasure for V4OUT Output
VLCD
Fixed
RV3
Vbp
current
source
Driver
V3OUT
C
GND
Figure 24-c Countermeasure for V3OUT Output
Note: The actual LCD drive voltage-VLCD used must not exceed 15.0 V, and the absolute rating must
not exceed 16.0 V.
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