Rev. 1.10

- 9 -

Tf

Formula 2

0

In this formula, Tf means the time of which the energy saved in the inductance is being emitted. Thus average

Tf

0

0

In PWM control, when Tf=Toff is true, the inductor current becomes continuos, then the operation of switching

regulator becomes continuous mode.

In the continuous mode, the deviation of the current is equal between on time and off time.

Formula 4

continuous. The continuous current through the inductor is described as Iconst, then,

Formula 6

In this moment, the peak current, ILxmax flowing through the inductor and the driver Tr. is described as follows:

×Ton/L

Formula 7

With the formula 4,6, and ILxmax is,

Formula 8

external components should be selected.

In the formula 7, peak current ILxmax at discontinuous mode can be calculated. Put Iconst=0 in the formula.

The explanation above is based on the ideal calculation, and the loss caused by Lx switch and external components

is not included. The actual maximum output current is between 50% and 80% of the calculation. Especially, when the

0.3V) of the diode should be considered.

Inverting DC/DC converter saves energy during on time of Lx transistor, and supplies the energy to output during off

time, output voltage opposed to input voltage is obtained.

Lx Tr

Inductor

Diode

CL

GND

i1

i2