[AP2403]

MS1528-E-02

2014/01

- 13 -

10.

Application Information

1. Inductance:

An external inductor must be selected so that the maximum ripple current will be 30% of the rated current.

The main power voltage (Vin) is the maximum value of input voltage range. The external inductor value is

determined by following equation.

2. Phase Compensation:

Resistors and a capacitor for phase compensation are connected between the CC pin and the Vref/SS pin.

Recommended values of these are shown below but they are not fixed. These values can be changed

according to the VIN and VOUT frequency settings to optimize the phase compensation.

(values shown below is in the case of “11. Recommended External Circuits”)

R4＝220[kΩ],

R5＝4.7[kΩ], C5=2200[pF]

3. Soft Start Time:

Soft-start time is determined by the C4 capacitor which is connected between the SS pin and the GND. The

relation of the capacitance and the soft-start time is calculated by the following equation.

Tss = C4／20×10

-6

[s]

4. Suspended Time in Hiccup Operation:

The suspended time in Hiccup operation is determined by the C4 capacitor which is connected between the

SS pin and the GND. The relation of the capacitance and the suspended time is calculated by the following

equation.

5. Output Voltage:

The output voltage is determined by the feedback resistors, and those two resistors are placed in series

between the output capacitor and the GND. Those resistor value of R2 (the output capacitor to FB pin) and

R1 (FB pin to GND) are calculated by the following equation.

Please note that the operation may become unstable by an influence of the switching noise when the current

which flows in the resistor becomes too small.

6. Oscillation Frequency:

The oscillation frequency is determined by the R3 resistor which is connected between the RT pin and the

GND. The relation of the resistor value and the oscillation frequency is calculated by the following equation.

]

H

[

Frequency

Vin

0.6

Vout

-

Vin

Vout

L

　　

）

（







]

s

[

10

1

C4

0.6

T

6

-

HIC

　　

＝









]

V

[

R1

R2

1

0.6

Vout

　　

　

＝





]

[

10

2.35

2

.

1

)

10

33

-

y

1/Frequenc

0.6

R3

12

-

-9

Ω

　　

（

＝　







