s-8460 Seiko Instruments Inc., s-8460 Datasheet - Page 12

• Manufacturer Part Number: s-8460
• Description: Step-up Or Down, Single-coil, Pwm Control Switching Regulator Controller
• Manufacturer: Seiko Instruments Inc.

12
STEP-UP OR DOWN, SINGLE-COIL, PWM CONTROL SWITCHING REGULATOR CONTROLLER
S-8460
2. Diode
3. Capacitors
4. External Transistors
3. 1 Input and Output Capacitors (C
3. 2 Internal Power Source Stabilization Capacitor (C
Continuous mode at step-up operation
Continuous mode at step-down operation
Where f
forward voltage. V
Use an external diode that meets the following requirements :
A capacitor inserted on the input side (C
stabilizing the input current. Select a C
capacitor that has low ESR (Equivalent Series Resistance) and large capacitance. Approximately 47 to 100 μF is
recommended for a capacitance depending on the impedance of the power source and load current value.
For the output side capacitor (C
When the input voltage is extremely high or the load current is extremely large, the output voltage may become
unstable. In this case the unstable area will become narrow by selecting a large capacitance for an output
capacitor. A tantalum electrolyte capacitor is recommended since the unstable area widens when a capacitor with
a large ESR, such as an aluminum electrolyte capacitor, or a capacitor with a small ESR, such as a ceramic
capacitor, is chosen.
Fully evaluate input and output capacitors under the actual operating conditions to determine the best value.
The main circuits of the IC work on an internal power source connected to the VL pin. C
for stabilizing the internal power source. C
low impedance.
Enhancement N-channel MOS FETs should be used for the external transistors.
SW1 is driven by the bootstrapped voltage. If a bipolar transistor is used for SW1, SW1 is not turned on since the
charge in the capacitor (C
• Low forward voltage (Schottky barrier diode is recommended.)
• High switching speed (50 ns)
• The current rating is larger than I
• The reverse-direction withstand voltage is higher than V
• The reverse-direction withstand voltage is higher than V
I
I
PK
PK
OSC
=
=
I
(= 300 kHz) is the oscillation frequency, L is the inductance value of the coil, and V
V
OUT
OUT
V
+
IN
+
V
F
2 fosc L V
OUT
V
should be approximately 0.4 V.
×
F
×
×
BST
I
(V
OUT
) for bootstrap is discharged.
× ×
IN
+
−
V
OUT
2 (V
(V
OUT
×
IN
), select a large capacitance with low ESR for smoothing the ripple voltage.
IN
OUT
PK
, C
)
.
OUT
IN
OUT
Seiko Instruments Inc.
+
value according to the impedance of the power supply used. Select a
V
VL
+
)
IN
F
V ) fosc L
) improves the efficiency by reducing the power impedance and
is a 4.7 μF ceramic capacitor and it should be wired nearby and at a
−
F
V ) V
×
IN
×
VL
)
×
IN
IN
IN
or V
for SD2.
OUT
for SD1.
VL
is a bypass capacitor
Rev.2.1
F
is the diode
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