s-8333aaca-t8t1g Seiko Instruments Inc., s-8333aaca-t8t1g Datasheet - Page 14

• Manufacturer Part Number: s-8333aaca-t8t1g
• Description: Step-up, For Lcd Bias Supply, 1-channel, Pwm Control Switching Regulator Controller
• Manufacturer: Seiko Instruments Inc.

14
STEP-UP, FOR LCD BIAS SUPPLY, 1-CHANNEL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
S-8333 Series
External Parts Selection
1. Inductor
2. Diode
3. Capacitors (C
The inductance has a strong influence on the maximum output current (I
The peak current (I
is decreased further, the efficiency falls, and I
transistor is insufficient.
The loss of I
certain L value. Further increasing L decrease the efficiency due to the loss of the DC resistance of the inductor.
I
If the oscillation frequency is higher, a smaller L value can be chosen, making the inductor smaller. In the S-8333
Series, the oscillation frequency can be varied within the range of 286 kHz to 1.133 MHz by the external resistor,
so select an L value best suited to the frequency. The recommended value is between 2.2 µH and 22 µH.
When selecting an inductor, note the allowable current of the inductor. If a current exceeding this allowable
current flows through the inductor, magnetic saturation occurs, substantially lowering the efficiency and
increasing the current, which results in damage to the IC.
Therefore, select an inductor so that I
equations in the discontinuous mode and continuous mode.
f
Use an external diode that meets the following requirements.
The capacitor on the input side (C
efficiency. Select C
The capacitor on the output side (C
value based on the I/O conditions and load conditions. A capacitance of 10 µ F or more is recommended.
By adjusting the phase compensation of the feedback loop using the external resistor (RZ) and capacitor (CZ), a
ceramic capacitor can be used as the capacitor on the output side. If a capacitor whose equivalent series
resistance is between 30 m Ω and 500 m Ω is used as the output capacitor, the adjustable range of the phase
compensation is wider; however, note that other characteristics may be affected by ripple voltage or other
conditions at this time. The optimal capacitor differs depending on the L value, capacitance value, wiring, and
application (output load), so select the capacitor after performing sufficient evaluation under the actual usage
conditions.
I
I
OUT
OSC
PK
PK
=
also decreases.
= Oscillation frequency, V
=
• Low forward voltage
• High switching speed
• Reverse breakdown voltage: V
• Rated current: I
V
OUT
2
V
I
OUT
PK
IN
+
IN
by the switching transistor decreases by increasing L and the efficiency becomes maximum at a
V
(V
, C
D
I
PK
OUT
fosc
OUT
L
IN
)
) increases by decreasing L and the stability of the circuit improves and I
according to the impedance of the power supply to be used.
PK
+
+
or more
L
(V
V
2
D
(V
OUT
−
D
OUT
≅ 0.4 V.
V
+
IN
V
+
IN
L
) is used to smooth the output voltage. Select an appropriate capacitance
)
PK
D
) can lower the supply impedance and level the input current for better
V
OUT
Seiko Instruments Inc.
−
D
does not exceed the allowable current. I
)
V
(
fosc
+ [Spike voltage] or more
discontinu
IN
)
OUT
V
L
IN
decreases if the current drive capability of the external
(continuou
ous
mode
s
)
mode)
.................................................................. (17)
........................................................ (18)
OUT
) and efficiency (η).
PK
is expressed by the following
OUT
increases. If L
Rev.2.3
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