
ZXSC300
Output Power Calculation
P OUT =
(V OUT V IN ) x ( I PK + I MIN ) T OFF
F =
By making the above assumptions for inductance and
peak current the output power can be determined by:
x
2 ( T ON + T OFF )
Note: V OUT = output voltage + Schottky rectifier voltage
drop
Operating frequency can be derived by:
1
( T ON + T OFF )
Capacitor selection
For pulsed operation, as in the maximum battery life
solution, no capacitors are required at the output to
the LED. For rectified operation, as in the maximum
brightness solution, a small value ceramic capacitor
is required, typically 2.2uF.
where
Generally an input capacitor is not required, but a
T OFF ? 1.7μs (internally set by ZXSC300)
and
small ceramic capacitor may be added to aid EMC,
typically 470nF to 1uF.
Demonstration board
T ON
=
T OFF ( V OUT ? V IN )
V IN
A demonstration board for the Maximum battery life
solution, is available upon request. These can be
obtained through your local Zetex office or through
and
I MIN = I PK ?
( V OUT - V IN ) x T OFF
L
Zetex web pages. For all reference designs Gerber
files and bill of materials can be supplied.
Layout of Maximum battery life solution
Top Copper
Bottom Copper
ISSUE 4 - SEPTEMBER 2007
9
Drill Holes
Silk Screen