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13.3.4
Step-Up Constant-Voltage (5 V) Power Supply
The H8/3867 Series has an on-chip step-up constant-voltage (5 V) power supply which enables a 5
V constant voltage to be obtained independently of V
H8/3827 Series.
When the SUPS bit is set to 1 in LCD control register 2 (LCR2), the step-up constant-voltage (5
V) power supply operates, and a 5 V constant voltage is output from the V
V
and V
pins or connect a resistance to divide the voltage.
0
1
Note: The step-up constant-voltage (5 V) power supply must not be used for any purpose other
than the H8/3864 Series' LCD drive power supply. When a large panel is driven, the power
supply capacity may be insufficient. In this case, either use V
an external power supply circuit.
13.3.5
Low-Power-Consumption LCD Drive System
The use of the built-in split-resistance is normally the easiest method for implementing the LCD
power supply circuit, but since the built-in resistance is fixed, a certain direct current flows
constantly from the built-in resistance's V
current dissipation of the LCD panel, if an LCD panel with a small current dissipation is used, a
wasteful amount of power will be consumed. The H8/3864 Series is equipped with a function to
minimize this waste of power. Use of this function makes it possible to achieve the optimum
power supply circuit for the LCD panel's current dissipation.
1. Principles
1. Capacitors are connected as external circuits to LCD power supply pins V1, V2, and V3,
as shown in figure 13-14.
2. The capacitors connected to V1, V2, and V3 are repeatedly charged and discharged in the
cycle shown in figure 13-14, maintaining the potentials.
3. At this time, the charged potential is a potential corresponding to the V1, V2, and V3 pins,
respectively. (For example, with 1/3 bias drive, the charge for V2 is 2/3 that of V1, and
that for V3 is 1/3 that of V1.)
4. Power is supplied to the LCD panel by means of the charges accumulated in these
capacitors.
5. The capacitances and charging/discharging periods of these capacitors are therefore
determined by the current dissipation of the LCD panel.
6. The charging and discharging periods can be selected by software.
. This feature is not provided in the
CC
to V
. As this current does not depend on the
CC
SS
348
pin. Either short the
0
as the power supply or use
CC
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