MAX1561 Datasheet, PDF(8/10 Page) Maxim Integrated Products – High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs

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MAX1561 Datasheet, PDF (8/10 Pages) Maxim Integrated Products – High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs

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High-Efficiency, 26V Step-Up Converters

for Two to Six White LEDs

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

higher cost. CCOMP stabilizes the converter and con-

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

to GND. For stable operation, COUT must not exceed

10 times CCOMP.

Inductor Selection

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

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

cy for most applications while maintaining low 15mVP-P

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:

IPEAK

VOUT(MAX) Ã ILED(MAX)

0.8 Ã VIN(MIN)

VIN(MIN) Ã 0.8Âµs

2ÃL

Schottky Diode Selection

The MAX1561/MAX1599sâ 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 diodeâs average and peak current rating

exceed the average output current and peak inductor

current. In addition, the diodeâs reverse breakdown volt-

age must exceed VOUT. The RMS diode current can be

calculated from:

IDIODE(RMS) â IOUT Ã IPEAK

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

the IC and RSENSE, the inductor, the diode, the input

capacitor, and the output capacitor. Keep traces short,

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

trace, away from CS. The IN bypass capacitor (CIN)

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

CIN and COUT should be as close together as possible.

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

8 _______________________________________________________________________________________

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