ZXSC300
Output Power Calculation
By making the above assumptions for inductance and
peak current the output power can be determined by:
P
OUT
=
(V
OUT-
V
IN
) x (I
PK
+
I
MIN
)
T
OFF
x
(T
ON
+
T
OFF
)
2
Operating frequency can be derived by:
1
F
=
(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.
Generally an input capacitor is not required, but a
small ceramic capacitor may be added to aid EMC,
typically 470nF to 1uF.
Demonstration board
T (V
−
V
IN
)
=
OFF OUT
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
Zetex web pages. For all reference designs Gerber
files and bill of materials can be supplied.
Note: V
OUT
= output voltage + Schottky rectifier voltage
drop
where
T
OFF
≅
1.7µs (internally set by ZXSC300)
and
T
ON
and
I
MIN
=
I
PK
−
( V
OUT
- V
IN
) x T
OFF
L
Layout of Maximum battery life solution
Top Copper
Drill Holes
Bottom Copper
Silk Screen
ISSUE 3 - NOVEMBER 2006
9
ZETEX [ ZETEX SEMICONDUCTORS ]
