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Rev. 1.11

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tonc=T

When ton<tonc, the mode is the discontinuous mode, and when ton=tonc, the mode is the continuous mode.

n OUTPUT CURRENT AND SELECTION OF EXTERNAL COMPONENTS

When LxTr is ON:

×××Equation 3

When LxTr is OFF:

L

×××Equation 4

Ripple Current is as follows;

wherein, peak current that flows through L, LxTr, and SD is as follows;

¼Equation 7

Consider ILmax, condition of input and output and select external components.

HThe above explanation is directed to the calculation in an ideal case in continuous mode.

n External Components

1. Inductor

Select an inductor that peak current does not exceed ILmax. If larger current than allowable current flows,

magnetic saturation occurs and make transform efficiency worse.

When the load current is same, the smaller value of L, the larger the ripple current.

Provided that the allowable current is large in that case and DC current is small, therefore, for large output current,

efficiency is better than using an inductor with a large value of L and vice versa.

2. Diode

3. Capacitor

mF for stable

operation.

COUT can reduce ripple of Output Voltage, therefore 47 to 100

mF tantalum type is recommended.

4. Lx Transistor

Pch Power MOS FET is required for this IC.

Its breakdown voltage between gate and source should be a few volt higher than Input Voltage.

In the case of Input Voltage is low, to turn on MOS FET completely, select a MOS FET with low threshold voltage.

If a large load current is necessary for your application and important, choose a MOS FET with low ON resistance

for good efficiency.

If a small load current is mainly necessary for your application, choose a MOS FET with low gate capacity for good

efficiency.

Maximum continuous drain current of MOS FET should be larger than peak current, ILmax.