MITSUBISHI MICROCOMPUTERS
3827 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
VOLTAGE MULTIPLIER (3TIMES)
The voltage multiplier performs threefold boosting. This circuit in-
puts a reference voltage for boosting from LCD power input pin
VL1. (However, when using a 1/2 bias, connect VL1 and VL2 and
apply voltage by external resistor division.)
Bias Control and Applied Voltage to LCD
Power Input Pins
To the LCD power input pins (VL1–VL3), apply the voltage shown in
Table 8 according to the bias value.
Select a bias value by the bias control bit (bit 2 of the LCD mode
register).
Set each bit of the segment output enable register and the LCD
mode register in the following order for operating the voltage mul-
tiplier.
Table 8 Bias control and applied voltage to VL1–VL3
1. Set the segment output enable bits (bits 0 to 5) of the seg-
ment output enable register to “0” or “1.”
Bias value
Voltage value
VL3=VLCD
2. Set the duty ratio selection bits (bits 0 and 1), the bias con-
trol bit (bit 2), the LCD circuit divider division ratio selection
bits (bits 5 and 6), and the LCDCK count source selection
bit (bit 7) of the LCD mode register to “0” or “1.”
3. Set the LCD output enable bit (bit 6) of the segment output
enable register to “1.”
1/3 bias
VL2=2/3 VLCD
VL1=1/3 VLCD
VL3=VLCD
1/2 bias
VL2=VL1=1/2 VLCD
Note 1: VLCD is the maximum value of supplied voltage for the
LCD panel.
4. Set the voltage multiplier control bit (bit 4) of the LCD mode
register to “1.”
When voltage is input to the VL1 pin during operating the voltage
multiplier, voltage that is twice as large as VL1 occurs at the VL2
pin, and voltage that is three times as large as VL1 occurs at the
VL3 pin.
When using the voltage multiplier, apply 1.3 V ≤ Voltage ≤ 2.3 V to
the VL1 pin.
When not using the voltage multiplier,apply proper voltage to the
LCD power input pins (VL1–VL3). Then set the LCD output enable
bit to “1.”
When the LCD output enable bit is set to “0,” the VCC voltage is
applied to the VL3 pin inside of this microcomputer.
The voltage multiplier control bit (bit 4 of the LCD mode register)
controls the voltage multiplier.
Contrast control
Contrast control
VCC
VCC
V
L3
L2
V
L3
L2
V
L3
R1
R2
R4
V
V
V
L2
2
C
C
2
1
C
C
2
1
Open
Open
C
Open
Open
C
V
1
VL1
VL1
L1
R3
R5
PX
X
R1=R2=R3
R4=R5
1/3 bias
1/3 bias
when not using the voltage multiplier
1/2 bias
when using the voltage multiplier
Fig. 40 Example of circuit at each bias
37
MITSUBISHI [ Mitsubishi Group ]
