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4.3 Controlling the Power Supply Circuit
In order to generate the internal operating voltage properly according to the power supply voltage and operating
mode, or to reduce current consumption, the power supply circuit is designed to be controlled with software.
Switching the operating mode
The S1C17704 has two kinds of operating modes.
1. Normal operation mode
This mode is provided for running the application program.
V
= 1.8 to 3.6 V, internal operating voltage V
DD
2. Flash erase/program mode
This mode is provided for erasing and programming the Flash memory.
V
= 2.7 to 3.6 V, internal operating voltage V
DD
The V
voltage value must be switched according to the operating mode as shown above using the VD1MD bit
D1
(D0/VD1_CTL register). Normally set VD1MD to 0 (V
erasing/programming the Flash memory.
∗ VD1MD: Flash Erase/Program Mode Bit in the V
Note: When the operating mode is switched, the internal operating voltage requires 5 ms (max.) to
stabilize. Flash memory programming should be started after the stabilization time has elapsed.
Controlling the LCD power source
The LCD system voltage regulator must be driven with a 2.5 V or more power voltage to generate appropriate
LCD drive voltages V
use the power voltage booster to generate double the V
with the V
output voltage. Set the PBON bit (D0/LCD_PWR register) to 1 to turn the power voltage booster
D2
on. In addition, set the VDSEL bit (D1/LCD_PWR register) to 1 to drive the LCD system voltage regulator
with the V
voltage output from the power voltage booster. PBON must be set to 1 before the drive voltage can
D2
be switched to V
.
D2
∗ PBON: Power Voltage Booster Control Bit in the LCD Power Voltage Booster Control (LCD_PWR) Register
(D0/0x50a4)
∗ VDSEL: Regulator Power Source Select Bit in the LCD Power Voltage Booster Control (LCD_PWR) Register
(D1/0x50a4)
When the power supply voltage (V
power voltage booster should be turned off to reduce current consumption. In this case, PBON and VDSEL are
both set to 0 (default).
Note: When the power voltage booster is turned on, the V
stabilize. Do not switch the power source for the LCD system voltage regulator to V
stabilization time has elapsed.
The LCD drive voltages V
LCD_DCTL register) to a value other than 0x0 (display off).
∗ DSPC[1:0]: LCD Display Control Bits in the LCD Display Control (LCD_DCTL) Register (D[1:0]/0x50a0)
When the internal LCD driver is not used, the power voltage booster and LCD system voltage regulator should
be turned off to reduce current consumption. Set PBON, VDSEL, and DSPC[1:0] to 0 (default).
S1C17704 TECHNICAL MANUAL
to V
. When the power supply voltage (V
C1
C5
) is 2.5 V or more, drive the LCD system voltage regulator with V
DD
to V
will be supplied to the LCD driver by setting the DSPC[1:0] bits (D[1:0]/
C1
C5
= 1.8 V
D1
= 2.5 V
D1
= 1.8 V, default setting). It should be set to 1 before
D1
Control (VD1_CTL) Register (D0/0x5120)
D1
) is within the range from 1.8 V to 2.5 V,
DD
voltage and drive the LCD system voltage regulator
DD
output voltage requires about 1 ms to
D2
EPSON
4 POWER SUPPLY
. The
DD
until the
D2
4-3
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