HD66724 Datasheet, PDF (72/117 Pages) Hitachi Semiconductor – (Graphics LCD Controller/Driver with Key Scan Function)

HD66724/HD66725
Contrast Adjuster
Contrast for an LCD can be adjusted by varying the liquid-crystal drive voltage (potential difference
between V_LCD and V1) through the CT bits of the contrast control instruction (electron volume function).
See figure 40 and table 37. The value of a variable resistor (VR) can be adjusted within a range from 0.1 x
R through 3.2 x R, where R is a reference resistance obtained by dividing the total resistance between V_LCD
and V1.
The HD66724/HD66725 incorporate a voltage-follower operational amplifier for each of V1 to V5 to
reduce current flowing through the internal bleeder-resistors, which generate different liquid-crystal drive
voltages. Thus, CT4-0 bits must be adjusted so that the potential differences between V_LCD and V1 and
between V5 and GND are 0.1 V or higher when liquid-crystal drives.
HD66724/5
VLCD
VR
CT
R
+
-
V1
R
+
-
V2
+
-
V3
R0
R
R
GND
+
-
V4
+
-
V5
GND
Figure 40 Contrast Adjuster
72