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Data Sheet S15726EJ2V0DS
37
μ
PD161401
5.6
Power Supply Circuit
5.6.1
Power supply circuit
The power supply circuit generates the voltage necessary for driving the LCD. The power circuit consists of a booster
circuit, voltage regulator circuit, and voltage follower circuit.
Power system control register 1 (R52) turns ON/OFF the transformer, reference voltage generator, voltage regulator
circuit (V regulator circuit), and voltage follower circuit (V/F circuit). Part of the internal power supply function and an
external power supply can be used in combination.
Table 5
12
shows the functions controlled by the 4-bit data of
power system control register 1 (R52).
Table 5
13
shows examples of combinations of the power circuit functions.
Table 5
12. Function of Each Bit of Power System Control Register
Status
Item
1
0
OP3
OP2
OP1
OP0
: Booster circuit control bit
: Reference voltage generator control bit
: Voltage regulator circuit (V regulator circuit) control bit
: Voltage follower circuit (V/F circuit) control bit
ON
ON
ON
ON
OFF
OFF
OFF
OFF
Table 5
13. Examples of Combinations (Reference Values)
Status
OP3
OP2
OP1
OP0
Booster
Circuit
Reference
voltage
V Regulator
Circuit
V/F
Circuit
External
Power Input
Booster
System Pins
<1> Only internal power supply is
used
1
1
1
1
Ο
Ο
Ο
Ο
V
DD2
Used
<2> External V
OUT
power supply
0
1
1
1
×
Ο
Ο
Ο
V
DD2,
V
OUT
Open
<3> Only V/F circuit is used
1
0
0
1
Ο
×
×
Ο
V
DD2,
AMP
OUT
Used
<4> Only external power supply is
used
0
0
0
0
×
×
×
×
V
DD2,
V
OUT
,
V
LCD
,
V
LC1
to V
LC4
Open
Remarks 1.
The “booster system pins” are the C
1
+
, C
1
to C
5
+
, C
5
pins.
2.
All the power circuits are turned OFF when the
μ
PD161401 serves as a slave (M,/S pin = L).
5.6.2
Booster circuit
The power supply circuit has an internal booster circuit that increases the LCD driver voltage two- to seven-fold.
Because this booster circuit uses the internal oscillator signals, either the oscillator must be operating or an external
display clock must be input to operate this circuit.
The booster circuit usually uses the C
1
+
, C
1
to C
5
+
, C
5
pins and V
DD2
pins. Keep the wiring impedance of these pins
as low as possible. The number of boosting steps for main duty display and sub-duty display is set as shown in
Table
5
14
by the MBT
n
and SBT
n
flags of power system control register 4 (R55).
For the number of boosting steps and how to connect capacitors, refer to
Figure 5
15
.