HD66750 Datasheet, PDF (59/96 Pages) Hitachi Semiconductor – 128 x 128-dot Graphics LCD Controller/Driver with Four-grayscale Functions

HD66750/1
Contrast Adjuster
Software can adjust 64-step contrast for an LCD by varying the liquid-crystal drive voltage (potential
difference between V_LCD and V1) through the CT bits of the contrast adjustment register (electron volume
function). The value of a variable resistor between V_LCD and V1 (VR) can be precisely adjusted in a 0.05 x
R unit within a range from 0.05 x R through 3.20 x R, where R is a reference resistance obtained by dividing
the total resistance.
The HD66750/1 incorporates 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, CT5-0 bits must be adjusted so that potential difference between V_LCD and V1 is 0.1 V or higher and
that between V4 and GND is 1.4 V or higher when liquid-crystal drives, particularly when the VR is small.
VLCD
HD66750/1
VR
CT
R
-+ ^V1
R
-+ ^V2
-+ ^V3
R0
R
R
GND
-+ ^V4
-+ ^V5
GND
Figure 40 Contrast Adjuster
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