S-8521F25MC-BPKT2G Seiko Instruments, S-8521F25MC-BPKT2G Datasheet - Page 18

• Manufacturer Part Number: S-8521F25MC-BPKT2G
• Description: IC REG PWM/PFM 300KHZ SOT23-5
• Manufacturer: Seiko Instruments
• Type: Step-Down (Buck)r

Specifications of S-8521F25MC-BPKT2G

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 2.5V
• Current - Output: 120mA
• Frequency - Switching: 300kHz
• Voltage - Input: 2.5 ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-5, SC-74A, SOT-25
• Power - Output: 250mW
• Output Voltage: 2.5 V
• Input Voltage: 2.5 V to 16 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

18
STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8520/8521 Series
2. Inductor
3. Diode
4. Capacitors (C
The inductance value (L value) has a strong influence on the maximum output current (I
The peak current (I
L value is decreased, the efficiency falls causing a decline in the current drive capacity for the switching transistor,
and I
The loss of I
certain L value. Further increasing L value decreases the efficiency due to the loss of the direct current resistance
of the coil. I
For the S-8520/8521 Series, increasing the inductance value, the output voltage may be unstable in some cases,
depending on the conditions of the input voltage, output voltage, and the load current. Perform sufficient evaluation
under the actual condition and decide an optimum inductance value.
The recommended inductances are 47 μH for A, B, C, D types and 22 μH for E, F types.
Be careful of the allowable inductor current when choosing an inductor. Exceeding the allowable current of the
inductor causes magnetic saturation, much lower efficiency and destruction of the IC chip due to a large current.
Choose an inductor so that I
following equation:
Use an external diode that meets the following requirements :
A capacitor for the input (C
Select the C
recommended for the capacitor depending on impedance of the power source and load current value.
For a capacitor for output (C
smoothing the ripple voltage. However, capacitor with extremely small ESR such as ceramic capacitor (about 0.3
Ω or less) may destabilize the output voltage, according to the conditions of input and output voltages. A
tantalum electrolyte capacitor is recommended. 47 μF to 100 μF is recommended for the capacitor.
I
*1.
*2.
• Its forward voltage is low (Schottky barrier diode is recommended).
• Its switching speed is high (50 ns max.).
• Its reverse direction voltage is higher than V
• Its current rating is higher than I
PK
OUT
= I
decreases.
f
V
OUT
osc
F
: Forward voltage of the diode
: Oscillation frequency
PK
+
OUT
IN
by the switching transistor decreases by increasing L and the efficiency becomes the maximum at a
(V
IN
also decreases.
2 × f
value according to impedance of the power supply to be used. Approximately 47 to 100 μF is
, C
OUT
PK
) increases by decreasing L value and the stability of the circuit improves and I
OUT
osc
+ V
*1
)
F
× L × (V
*2
) × (V
PK
IN
) improves efficiency by reducing power impedance and stabilizing the input current.
does not exceed the allowable current. I
L
), select a large capacitance with low ESR (Equivalent Series Resistance) for
IN
IN
+ V
− V
PK
.
F
OUT
*2
)
)
Seiko Instruments Inc.
IN
.
PK
in continuous mode is calculated by the
OUT
) and efficiency (η).
OUT
Rev.9.0
increases. If
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