SIC63616-(Rev. 1.0) NO. P33
3240-0412
4.2.2 Controlling the power supply voltage booster/halver and voltage regulators
Controlling the power supply voltage booster/halver
The power supply voltage booster/halver generates the operating voltage V
D2
for driving the voltage
regulator (LCD system voltage regulator) when the supply voltage V
DD
is out of their operating voltage
range.
The power supply voltage booster/halver has two operating modes, boost mode and halving mode,
that can be selected using the DBON and HLON registers according to the V
DD
value being supplied.
The power supply voltage booster/halver enters boost mode by setting DBON to "1" and boosts the
supply voltage V
DD
to generate V
D2
(about double V
DD
). The power supply voltage booster/halver
should be placed in boost mode only when V
D2
is required for driving the LCD system voltage regula-
tor (see "Controlling the LCD system voltage regulator" described below).
HLON is prohibited from use. Always be sure to set to "0".
Setting both DBON and HLON to "0" turns the power supply voltage booster/halver off. The V
D2
volt-
age is not required when the supply voltage V
DD
is within the range from 2.5 V to 5.5 V (1.6 V to 5.5
V when the V
C1
reference LCD drive power option is selected). In this case the power supply voltage
booster/halver should be turned off to reduce current consumption.
At initial reset, DBON and HLON are both set to "0" and the power supply voltage booster/halver does
not activate.
Controlling the LCD system voltage regulator
When the V
C2
reference LCD drive power option is selected, the LCD system voltage regulator must be
driven with a 2.5 V or more power voltage. Therefore, they can be driven with V
DD
if the supply voltage
V
DD
is 2.5 V or more. When the supply voltage V
DD
less than 2.5 V is used, drive the power supply volt-
age booster/halver in boost mode to generate V
D2
and use it to drive the LCD system voltage regulator.
Use VCSEL to select the power source voltage (V
DD
or V
D2
) for the LCD system voltage regulator. It is
driven with V
DD
by setting VCSEL to "0" or V
D2
by setting VCSEL to "1".
At initial reset, VCSEL is set to "0" so that V
DD
is selected as the power source for the LCD system volt-
age regulator.
To generate the LCD drive voltages by the LCD system voltage regulator (to start LCD display), turn the
LCD system voltage regulator on using the LPWR register. When "1" is written to LPWR, the LCD sys-
tem voltage regulator goes on and generates the LCD drive voltages. At initial reset, LPWR is set to "0"
(Off). When LCD display is not necessary, turn the LCD system voltage regulator off to reduce power
consumption.
Notes: • When driving the LCD system voltage regulator with V
D2
, be sure to write "1" to DBON to place
the power supply voltage booster/halver in boost mode before setting VCSEL to "1". Furthermore,
do not switch the power source to V
D2
for about 1 msec until the V
D2
voltage has stabilized after
the power supply voltage booster/halver is turned on.
• Do not set DBON to "1" (boost mode) and VCSEL to "1" (driving with V
D2
) if the supply voltage
V
DD
exceeds 2.5 V, as it may cause damage of the IC.
• If V
DD
less than 2.5 V is used as the power source for the LCD system voltage regulator, the V
C1
to V
C5
voltages cannot be generated within specifications (when a V
C2
reference voltage option is
selected).