MP1523 datasheet(5/7 Pages) MPS

5 / 7 page

MP1523 – PRECISION 6-LAMP WHITE LED DRIVER

INITIAL RELEASE

07/04, Rev. 1.6

www.MonolithicPower.com

APPLICATIONS INFORMATION

Setting the LED current

The LED current is set by the sense resistor

(R2) at FB. The LED current can be calculated

as:

LED =

Where VFB is 400mV. The LED current is set to

20mA if R2 = 20Ω.

Capacitor Selection

A 1µF to 10µF ceramic input capacitor (C1) and

a 0.47µF to 1µF ceramic output capacitor (C2)

are recommended for most applications. A

capacitor (typically 1nF) in parallel with the LED

string improves stability, input and output ripple

especially when large inductance values (10µH

or above) are used. For best stability over a

wide temperature range, use capacitors with an

X5R or X7R dielectric.

Inductor selection

The MP1523 has a 450mA inductor current limit

and can drive up to 6 LEDs at 20mA.

Inductance values (L1) from 4.7µH to 47µH

work satisfactorily. Larger values provide the

best efficiency while small inductor values allow

the smallest inductor size. To prevent

saturation, use an inductor with a saturation

current rating that matches the device current

limit.

Diode selection

The

MP1523’s

high

switching

frequency

demands a high-speed rectifier (D1) for

optimum efficiency. A schottky diode is

recommended due to its fast recovery time and

low forward voltage drop. Ensure the diode’s

average and peak current ratings exceed the

average output current and peak inductor

current. In addition, the diode’s reverse

breakdown voltage must exceed the output

voltage.

Layout

Careful PC board layout is required due to fast-

switching. All components must be placed as

close to the IC as possible. Keep the path

between inductor L1, diode D1, and output

capacitor C2 extremely short for minimal noise

and ringing. The feedback components such as

sense resistor R2 must be kept close to the FB

pin to prevent noise injection on the FB pin

trace. The ground return of C1 and C2 should

be tied close to the GND pin. See the MP1523

demo board layout for reference.

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