MP1528DK MPS [Monolithic Power Systems], MP1528DK Datasheet - Page 7

• Manufacturer Part Number: MP1528DK
• Description: 9 Lamp, 36V Precision White LED Driver
• Manufacturer: MPS [Monolithic Power Systems]

APPLICATION INFORMATION
Setting the LED Current
The LED current is set by the voltage at BRT
(V
V
0.27V to 1.2V. Over this range, the LED current
can be calculated as:
Voltages greater than 1.2V can be applied to
BRT. Use 1.2V in the equation if V
the BRT pin is left open.
For example, the LED current is set to 20mA if
V
Capacitor Selection
A 4.7µF to 10µF ceramic input capacitor (C1)
and a 0.47µF to 1µF ceramic output capacitor
(C2) are recommended for most applications. A
capacitor (C3, typically 1nF to 10nF) in parallel
with the LED string improves stability, input
ripple and output ripple, especially when large
inductance values (10µH or above) are used.
For the best stability over a wide temperature
range, use capacitors with a X5R or X7R
dielectric.
Inductor Selection
The MP1528 has a 950mA inductor current limit
and can drive up to 9 LEDs at 20mA.
Inductance values (for L1) from 4.7µH to 22µH
will work as well. 6.2µH or 6.8µH is a good
choice for high efficiency and small size. To
prevent saturation, use an inductor with a
saturation current rating that is higher than the
device current limit.
MP1528 Rev. 1.7
2/21/2006
BRT
BRT
BRT
≥ 1.2V (or left open) and R1 = 20Ω.
) and the sense resistor (R1) at FB. The
range for adjusting the LED current is
TM
I
LED
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
=
3
V
×
BRT
R
1
BRT
≥ 1.2V or
© 2006 MPS. All Rights Reserved.
www.MonolithicPower.com
MP1528 – 9 LAMP, 36V PRECISION WHITE LED DRIVER
Diode Selection
The
demands a high speed rectifier (D1) for
optimum
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.
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 the inductor L1, diode D1, and output
capacitor C2 extremely short for minimal noise
and ringing. The feedback components such as
the sense resistor R1 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 MP1528
demo board layout for reference.
MP1528’s
In
efficiency.
addition,
high
A
the
switching
Schottky
diode’s
frequency
diode
reverse
is
7