S-8331 Seiko Instruments USA, S-8331 Datasheet - Page 20

• Manufacturer Part Number: S-8331
• Description: Step-Up Switching Regulator (DC/DC Converter ICs)
• Manufacturer: Seiko Instruments USA

20
STEP-UP, FOR LCD BIAS SUPPLY, 1-CHANNEL SWITCHING REGULATOR
S-8330/8331 Series
I
OUT
S-8330A
2. Inductor
Figure 12 shows the dependency of I
The inductance value greatly affects I
The smaller value L, the larger peak current I
When decreasing value L further, the switching transistor falls short of the current drive ability and I
decreases; when increasing value L, a loss due to I
efficiency reaches the maximum in a certain value L; when increasing value L, a loss due to a series
resistor of the coils increases. This worsens the efficiency. So, it is recommended to set value L to 22
to 100 μH in the S-8330A and 47 to 220 μH in the S-8330B, respectively.
Determine value L referring to the reference data because the maximum output current actually differs
depending upon the input voltage.
Pay attention to the allowable current of the inductor when selecting an appropriate inductor. If current
exceeding this allowable current flows into the inductor, magnetic saturation occurs in the inductor.
This may lead to a serious drop in the efficiency and damage of the IC due to exessive current.
Select an appropriate inductor so that I
continuous mode is represented by the following equation.
Where f
power source of input voltage V
8330A30FS responds to your requirements because f
I
value L is 47 μH and the allowable current is 174 mA or more.
A limitation relating to the maximum value I
less.
I
PK
PK
=174 mA is found out as shown in equation (17). As a result, you can select an inductor for which
=
2
Figure 12 Dependency of Inductance On Maximum Output Current and Efficiency
OSC
Recommended Range
22
I
OUT
LQH4N
V
I
OUT
is the oscillating frequency. Set V
OUT
(
V
=18V, V
F
OUT
OSC
+
•
100
L
IN
V
=5.0V
D
−
V
IN
)
L value (μH)
η
IN
=5 V, output voltage V
(A)
Seiko Instruments Inc.
OUT
OUT
PK
, η of the S-8330A and the S-8330B on “L”.
and efficiencyη.
η
does not exceed this allowable current. Current I
PK
PK
D
lies in the IC itself. Always use current I
. I
to approximately 0.4 V. For example, when you want a
OUT
I
OUT
S-8330B
PK
reaches the maximum value in a certain value L.
of the switching transistor decreases and the
OSC
OUT
=180 kHz. When you set value L to 47 μH,
=30 V, and load current I
LQH4N
V
(17)
I
Recommended Range
OUT
OUT
47
=18V, V
IN
=5.0V
220
η
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OUT
PK
L value (μH)
=5 mA, the S-
Rev.5.1
at 500 mA or
PK
in the non-
η
OUT
_00