input and output ripple, but at the expense of size and

trols soft-start. Connect a 0.1µF capacitor from COMP

Inductor Selection

Inductor values range from 10µH to 47µH. A 22µH

(47µH for the MAX1599) inductor optimizes the efficien-

input ripple. With input voltages near 5V, a larger value

of inductance can be more efficient. To prevent core

saturation, ensure that the inductor-saturation current

rating exceeds the peak inductor current for the appli-

cation. Calculate the peak inductor current with the fol-

lowing formula:

Schottky Diode Selection

The MAX1561/MAX1599s’ high switching frequency

demands a high-speed rectification diode (D1) for opti-

mum efficiency. A Schottky diode is recommended due

to its fast recovery time and low forward-voltage drop.

Ensure that the diode’s average and peak current rating

exceed the average output current and peak inductor

current. In addition, the diode’s reverse breakdown volt-

calculated from:

Applications Information

PC Board Layout

Due to fast switching waveforms and high-current

paths, careful PC board layout is required. An evalua-

tion kit (MAX1561EVKIT) is available to speed design.

Order MAX1599 samples separately.

When laying out a board, minimize trace lengths between

capacitor, and the output capacitor. Keep traces short,

direct, and wide. Keep noisy traces, such as the LX node

should be placed as close to the IC as possible. PGND

and GND should be connected directly to the exposed

paddle underneath the IC. The ground connections of

The traces from IN to the inductor and from the Schottky

diode to the LEDs may be longer.

Chip Information

TRANSISTOR COUNT: 2895

PROCESS: BiCMOS

II

I

DIODE RMS

OUT

PEAK

I

VI

V

Vs

L

PEAK

OUT MAX

LED MAX

IN MIN

IN MIN

=

×

×

+

×µ

×

()

()

()

()

.

.

08

08

2

High-Efficiency, 26V Step-Up Converters

for Two to Six White LEDs

8

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