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(2)
Example of using the DDCK2 external doubler transistor
The DDCK2 pin outputs the DC-DC converter clock in the CMOS type. The external transistor is used to increase
the voltage like the DDCK1 pin. The doubled voltage can be set freely by using the external transistor. When the
DDCK2 pin is used, set the POL bit to "1".
Shown below is an example of a DC-DC converter circuit using the DDCK2 pin. Determine the R1/R2 resistance
according to your desired doubled voltage. The P8-0 pin control is the same as for the DDCK1 pin.
Voltage of DC-DC converter for VT
VT用DC-DCコンバータ電圧
Power supply
電源
電源
(V
)
（ VDD)
DD
+
-
Note:
Determine the doubler coil constant depending on the DC-DC converter clock frequency and
the doubler current capacity.
Note:
It doesn't matter if a zener diode is used as a substitute for the clamp circuit (VDET). Using the
zener diode eliminates the need to use the VDET and doubler on/off control pins (P8-2).
Note:
Add the charge up capacitor for the base input of the external transistor when the doubler
capacity is insufficient.
Note:
When the doubler function is turned off by using pin P8-2, turn it off when the voltage of the
DC-DC converter for VT has decreased sufficiently. A high voltage is applied to pin P8-2, and
this may cause damage.
Note:
The prebuffer power supply for the DDCK2 pin output uses a V
allowing stable doubler operation, even if the V
power supply level is outputted as the "H" level of the DDCK2 pin output.
Note:
The filter circuit constants shown above are for reference only. Examine and design actual
circuits according to your desired characteristics.
Note
注
0.01uF
～
DDCK2
57
4.7kΩ
100uH
VDET
58
59
60
R1
R2
～
外部DC-DCトランジスタ昇圧回路例
Example of external DC-DC transistor doubler circuit
112
V
VLCD
LCD
Clock of DC-DC converter for VT
VT用DC-DCコンバータクロック
+
-
0.75V
VDB
V
DB
P8-2 (ON: "L" output, OFF: HZ)
P8-2(ON:"L"出力 OFF:HZ)
、
LCD
power supply is reduced. Note that the V
DD
TC9349AFG
(3 V) pin power supply,
DD
2006-02-24
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