HD66724 Datasheet, PDF (75/117 Pages) Hitachi Semiconductor – (Graphics LCD Controller/Driver with Key Scan Function)

HD66724/HD66725
Liquid Crystal Display Drive Bias Selector Circuit
An optimum liquid crystal display bias value can be selected using BS2-0 bits, according to the liquid
crystal drive duty ratio setting (NL2-0 bits). Liquid crystal display drive duty ratio and bias value can be
displayed while switching software applications to match the LCD panel display status. The optimum bias
value calculated using the following expression is an ideal value where the optimum contrast is obtained.
Driving by using a lower value than the optimum bias value provides lower contrast and lower liquid
crystal display voltage (potential difference between V1 and GND). When the liquid crystal display
voltage is insufficient even if a triple booster is used or output voltage is lowered because the battery life
has been reached, the display can be made easier to see by lowering the liquid crystal bias.
The liquid crystal display can be adjusted by using the contrast adjustment register (CT4-0 bits) and
selecting the booster output level (BT1/0 bits).
Optimum bias value for 1/N duty ratio drive voltage =
Table 39 Optimum Drive Bias Values
1
N +1
LCD drive duty ratio
(NL2-0 set value)
Optimum drive bias value
(BS2-0 set value)
1/26 duty ratio
(NL2-0 = 011)
1/6 bias
(BS2-0 = 001)
1/18 duty ratio
(NL2-0 = 010)
1/5 bias
(BS2-0 = 011)
1/10 duty ratio
(NL2-0 = 001)
1/4 bias
(BS2-0 = 101)
1/2 duty ratio
(NL2-0 = 000)
1/4 bias
(BS2-0 = 101)
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