Chapter 14
LCD Functions
Operation
XIV - 15
14-3-3
Power Supply
The LCD driver power pins are VLC1, VLC2 and VLC3. This LSI contains the internal voltage booster circuit
as a dedicated power source for LCD drive and the voltage divider resistor to divide voltage for LCD
drive. There are three ways to supply voltage to the LCD driver; to supply voltage to the VLC1, VLC2 and
VLC3 pins from external source (when external voltage divider resistor is used), to supply voltage to VLC1
pin from external source and use internal divider resistor, and to supply voltage to the VLC2 or VLC3 pin
from external source and use the internal voltage divider resistor.
The power source for LCD drive and VDD power supply for the microcontroller are separated so that the
voltage VDD for LCD panel drive can be used at higher voltage than the VDD power supply (usable at VDD
≤ VLCD ≤ 5.5 V).
The LCD driver voltage supplied through the LCD driver power pins (VLC1, VLC2 and VLC3) is converted by
the LCD clock signal and the timing control signal, and then supplied to the segment driver and the
common driver.
Supplying voltage with the external voltage divider resistor
Table 14-3-1 LCD Power Supply
VLC1
VLC2
VLC3
VLCD: LCD panel driver voltage (Maximum voltage to the LCD panel)
Static
1/2
1/3
Bias
Method
LCD
Power Supply
VLCD + VSS
VSS
1/2VLCD + VSS
VLCD + VSS
1/3 VLCD + VSS
2/3 VLCD + VSS
VLCD + VSS
Use the LCD panel driver voltage VLCD at VDD
≤ VLCD ≤ 5.5 V.
When internal divider resostor is used, voltages of VLC1, VLC2, and VLC3 could be dropped
depending on used LCD panel, and that may lower the brightness of LCD display. Use the
external divider resistor when this happens.
When LCD function is used without voltage booster circuit (when voltage is supplied to the
VLC1, VLC2 and VLC3 pins from external source and internal voltage devider resistor is used),
fix C1 and C2 pins to following potential.
C1=VLC3
C2=VLC1