R1211D103C datasheet(11/40 Pages) RICOH

11 / 40 page

R1211x

When IOUT becomes more than formula 5, the current flows through the inductor, then the mode becomes

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

{}

OUT

OSC

OUT

Iconst/V

)

−

...............................................................Formula 6

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

follows:

Iconst

ILxmax

.................................................................................................................Formula 7

With the formula 4,6, and ILxmax is,

/(2

ILxmax

OUT

..............................................................................................Formula 8

Therefore, peak current is more than IOUT. Considering the value of ILxmax, the condition of input and output,

and 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 ILx is large, or VIN is low, the loss of VIN is generated with the on resistance of the switch. As

for VOUT, Vf (as much as 0.3V) of the diode should be considered.

R1211D103C Datasheet(PDF) 11 Page - RICOH electronics devices division