Rev. 1.12

- 10 -

tonc =T

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

s OUTPUT CURRENT AND SELECTION OF EXTERNAL COMPONENTS

When P-channel Tr. of Lx is ON:

⋅⋅⋅Equation 3

When P-channel Tr. of Lx is “OFF”(N-channel Tr. is “ON”):

L

⋅⋅⋅Equation 4

Ripple Current is as follows;

…Equation 6

wherein, peak current that flows through L, and Lx Tr. is as follows;

…Equation 7

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

5The above explanation is directed to the calculation in an ideal case in continuous mode.

×(R1+R2)/R2

Thus, with changing the value of R1 and R2, output voltage can be set in the specified range.

In the DC/DC converter, with the load current and external components such as L and C, phase might be behind 180

degree. In this case, the phase margin of the system will be less and stability will be worse. To prevent this, phase

margin should be secured with proceeding the phase. A zero is formed with R1, R2, and Cb.

Fpole

≅Fzero∼1/(2π×(R1+R2)×Cb)

Considering external components, LC, set the appropriate value of R1+R2 and Cb.

Ω.

When the R1

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.

Supposed that the load current is at the same, the smaller value of L is used, the larger the ripple current is.

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. Capacitor