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CHAPTER 18 LCD CONTROLLER/DRIVER
User’s Manual U15798EJ2V0UD
18.7 Supplying LCD Drive Voltages V
LCD0
, V
LCD1
, and V
LCD2
The
µ
PD780344, 780354, 780344Y, 780354Y Subseries contains a booster circuit (
×
3 only) to generate a supply
voltage to drive the LCD. The internal LCD reference voltage (V
LCD2
) is output from the V
LC2
pin. A voltage two times
higher than that on V
LCD2
(V
LCD1
) is output from the V
LC1
pin and a voltage three times higher than that on V
LCD2
(V
LCD0
)
is output from the V
LC0
pin.
The LCD reference voltage (V
LCD2
) can be varied by setting LCD gain adjust register 0 (VLCG0) as listed in Table
18-6.
In addition, an external capacitor (recommended value: 0.47
µ
F) is required because a capacitance division method
is employed to generate the supply voltage to drive the LCD.
Table 18-6. Output Voltages of V
LC0
to V
LC2
Pins
VLCG0
GAIN = 0
GAIN = 1
LCD Driving Power Supply Pin
V
LC0
pin
3.0 V
4.5 V
V
LC1
pin
2.0 V
3.0 V
V
LC2
pin (LCD reference voltage)
1.0 V
1.5 V
Cautions 1. When using the LCD function, do not leave the V
LC0
, V
LC1
, and V
LC2
pins open. Refer to Figure
18-12 for connection.
2. A constant LCD drive voltage can be supplied regardless of changes in V
DD
.
Remark
For the LCD reference voltage (V
LCD2
), refer to the LCD controller driver characteristics in
CHAPTER
25 ELECTRICAL SPECIFICATIONS
.
Figure 18-12. Example of LCD Driver Pin Connection
Remark
Use a capacitor with as little leakage as possible. Use a nonpolar capacitor as C1.
V
LC0
V
LC1
V
LC2
C2
C3
C4
CAPH
C1
External pin
CAPL
C1 = C2 = C3 = C4 = 0.47 F
µ
