MP1523 – PRECISION 6-LAMP WHITE LED DRIVER
INITIAL RELEASE
APPLICATIONS INFORMATION
Setting the LED current
saturation, use an inductor with a saturation
current rating that matches the device current
limit.
The LED current is set by the sense resistor
(R2) at FB. The LED current can be calculated
as:
Diode selection
The MP1523’s high switching frequency
demands a high-speed rectifier (D1) for
VFB
ILED
=
R2
optimum efficiency.
A
schottky diode is
Where VFB is 400mV. The LED current is set to
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.
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.
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.
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
07/04, Rev. 1.6
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