R1282D002A Datasheet, PDF (7/18 Pages) RICOH electronics devices division – 2CH PWM DC/DC CONTROLLER

R1282D002A
In this moment, the peak current, ILXmax flowing through the inductor and the driver Tr. is described as
follows:
ILXmax = Iconst +VIN×Ton/L........................................................................................... Formula 7
With the formula 4,6, and ILXmax is,
ILXmax = VOUT/VIN×IOUT+VIN×Ton/(2×L)........................................................................... 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.
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