HD66740 Datasheet, PDF (46/95 Pages) Hitachi Semiconductor – 112 x 80-dot Graphics LCD Controller/Driver

HD66740
When an Internal Booster and Internal Operational Amplifiers are Used
To supply LCD drive voltage using the internal booster, circuits should be connected as shown in figure
23. Here, contrast can be adjusted through the CT bits of the contrast control instruction. Temperature can
be compensated either through the CT bits or by controlling the reference voltage for the booster (Vci
pin) using a thermistor.
Note that Vci is both a reference voltage and power supply for the booster. The reference voltage must
therefore be adjusted using an emitter-follower or a similar element so that sufficient current can be
supplied. In this case, Vci must be equal to or smaller than the V_CC level.
The HD66740 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, the potential differences between V_LCD and V1 and between V5 and GND must be 0.4 V
or higher.
Note that the OPOFF pin must be grounded when using the operational amplifiers. Place a capacitor of
about 0.1 µF to 0.5 µF between each internal operational amplifier V1OUT to V5OUT output and GND
and stabilize the output level of the operational amplifier.
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