HD66727 Datasheet, PDF (66/97 Pages) Hitachi Semiconductor – Low-Power Dot-Matrix Liquid Crystal Display Controller/Driver with Key Scan Function

HD66727
Contrast Adjuster
Multiplexing Drive System
Contrast for an LCD controlled by the multiplexing drive method can be adjusted by varying the liquid-
crystal drive voltage (potential difference between V_CC and V5) through the CT bits of the contrast control
instruction (electron volume function). See Figure 38 and Table 30. The value of a variable resistor (VR)
can be adjusted within the range from 0.4 x R through 6.4 x R, where R is a reference resistance obtained
by dividing the total resistance between V_CC and V5.
The HD66727 incorporates a voltage-follower operational amplifier for each of V1 to V5 to reduce current
flowing through the internal bleeder-resistors, which generate different levels of liquid-crystal drive
voltages. Thus, potential differences between V_CC and V1 and between V_EE and V5 must be 0.4V or greater.
Note that the OPOFF pin must be grounded when using the operational amplifiers.
1/6 bias (V2 and V3 pins left open):
LCD drive voltage VLCD: 6R × (V_CC – V_EE)/(6R + VR) (VR = a value within the range from 0.4R to
6.4R)
VLCD adjustable range: 0.484 × (V_CC – V_EE) ≤ VLCD ≤ 0.938 × (V_CC – V_EE)
Potential difference between V_CC and V1: R × (V_CC – V_EE)/(6R + VR) ≥ 0.4 (V)
Potential difference between V5 and V_EE: VR × (V_CC – V_EE)/(6R + VR) ≥ 0.4 (V)
1/4 bias (V2 and V3 pins short-circuited):
LCD drive voltage VLCD: 4R × (V_CC – V_EE)/(4R + VR) (VR = a value within the range from 0.4R to
6.4R)
VLCD adjustable range: 0.385 × (V_CC – V_EE) ≤ VLCD ≤ 0.909 × (V_CC – V_EE)
Potential difference between V_CC and V1: R × (V_CC – V_EE)/(4R + VR) ≥ 0.4 (V)
Potential difference between V5 and V_EE: VR × (V_CC – V_EE)/(4R + VR) ≥ 0.4 (V)
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