Rainbow Electronics MAX1583 - Manual (Page 9)

MAX1583
White LED Camera-Flash
Boost Converter
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Input-Capacitor Selection
Bypass the input to GND using a ceramic capacitor.
Place the capacitor as close to the IC as possible. The
exact value of the input capacitor is not critical. The
typical value for the input capacitor is 22µF when using
the MAX1583X, 10µF when using the MAX1583Y, and
4µF when using the MAX1583Z. Using these values
reduces the input ripple to an acceptable level.
Output-Capacitor Selection
The output capacitance required depends on the
required LED current and the time duration of the pulse
in strobe mode. See the Reservoir Capacitance vs.
Current Limit section for details on determining this
capacitance value. Note that the output capacitor must
be rated for 25V or greater. In addition to the reservoir
capacitor, bypass the output with a 0.1µF, 25V capaci-
tor from OUT to LED.
Inductor Selection
The recommended inductor values for use with the
MAX1583 range from 4.7µH to 47µH. With input volt-
ages near 5V, a larger value of inductance can be
more efficient. To prevent core saturation, ensure that
the inductor-saturation current rating exceeds the cur-
rent limit of the MAX1583 (250mA, 500mA, or 1A).
Schottky-Diode Selection
The MAX1583 requires a high-speed rectification diode
(D1) for optimum performance. A Schottky diode is rec-
ommended due to its fast recovery time and low for-
ward-voltage drop. Ensure that the diode’s average
and peak current ratings exceed the average output
current and the current limit (I
LIMIT ) of the MAX1583
(250mA, 500mA, or 1A). In addition, the diode’s reverse
breakdown voltage must exceed V
OUT . The RMS diode
current is calculated as:
Applications Information
PC Board Layout
Due to fast-switching waveforms and high-current
paths, careful PC board layout is required. An evalua-
tion kit (MAX1583EVKIT) is available as an example to
speed design. When laying out a board, minimize trace
lengths between the IC and the inductor, the diode, the
input capacitor, and the output capacitor. Keep traces
short, direct, and wide. The IN bypass capacitor should
be placed as close to the IC as possible. GND should
be connected directly to the exposed paddle under-
neath the IC. The ground connections of C
IN and C OUT
should be as close together as possible. The traces
from IN to the inductor and from the Schottky diode to
the LEDs can be longer.
Chip Information
TRANSISTOR COUNT: 1395
PROCESS: BiCMOS
I I I
DIODE RMS LED MAX LIMIT ( ) ( )
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