AME5144 Datasheet, PDF(9/15 Page) AMETHERM Circuit Protection Thermistors – High Efficiency, 37V Step-Up Converter for 2 to 10 White LEDs

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AME5144 Datasheet, PDF (9/15 Pages) AMETHERM Circuit Protection Thermistors – High Efficiency, 37V Step-Up Converter for 2 to 10 White LEDs

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AME

AME5144

High Efficiency, 37V Step-Up

Converter for 2 to 10 White LEDs

Capacitor Selection

Schottky Diode Selection

Ceramic capacitors with X5R, X7R, or better dielectric

are recommended for stable operation over the entire op-

erating temperature range. The exact values of input and

output capacitors are not critical. The typical value for

input capacitor is 2.2ÂµF, and the typical value for output

capacitor is 0.1ÂµF. Higher values capacitors can be used

to reduce input and output ripple, but at the expense of

size and higher cost. CCOMP stabilizes the converter and

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

to GND.

The high switching frequency of the AME5144 demands

a high-speed rectification diode (D1) for optimum 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 out-

put current and peak inductor current. In addition, the

diode's reverse breakdown voltage must exceed VOUT. The

RMS diode current can be approximated from:

I = DIODE(RMS) I OUT Ã I PEAK

Inductor Selection

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

ductor optimizes the efficiency for most applications while

maintaining low 12mVp-p input ripple. Inductor with low

DCR can be more efficiency. To prevent core saturation,

ensure that the inductor-saturation current rating exceeds

the peak inductor current for the application. Calculate

the peak inductor current with the following formula:

I PEAK

V Ã I OUT (MAX ) LED(MAX )

0.9Ã VIN (MIN )

VIN(MIN ) Ã 0.9us

2Ã L

200mA, 40V Schottky diode SOD-523 or Central Semi-

conductor CMOSH-4E are recommended for applications.

Layout Consideration

Due to fast switching waveforms and high-current paths,

careful PC board layout is required. When laying out a

board, minimum trace lengths between the IC and RSENSE,

the inductor, the diode, the input capacitor and output ca-

pacitor. Keep trace short and wide. Keep noisy traces,

such as the SW node trace, away from CS.

22ÂµH, 250mA inductor Murata LQH32CN220K and The input bypass capacitor CIN should be placed as close

Sumida CDRH5D16NP- 220MB are recommended.

C to the IC as possible. This will reduce copper trace resis-

tance, which effect the input voltage ripple of the IC. The

output capacitor, COUT, should also be placed close to the

i e IC and connected directly between the OUT and GND pins.

PGND and GND should be connected directly to the ex-

posed paddle underneath the IC. The ground connections

of CIN and COUT should be as close together as possible.

Any copper trace connections with the COUT capacitor can

increase the series resistance which directly effects out-

put ripple and efficiency. The current setting resistor,

RSENSE, should be kept close to the CS pin to minimize

copper trace connections that can inject noise in to the

system. The traces from IN to the inductor and from

Schottky diode to the LEDs can be longer.

Rev.D.01

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