MP2483 – 2.5A, 55V, PROGRAMABLE FREQUENCY WHITE LED DRIVER
MP2483 Rev. 1.0 www.MonolithicPower.com 10
12/25/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
APPLICATION INFORMATION
Setting the LED Current
The external resistor is used to set the
maximum LED current (see the schematic on
front page) through the use of the equation:
=
Setting the Operating Frequency
The resistor on RSET pin is used to set the
operating frequency. A 1nF capacitor is
recommended to bypass this pin to GND.
The relationship between the operating
frequency and the RSET resistor is as the
following curve. A 20k to 150k RSET
resistor is recommended, which sets the
operating frequency from around 1.3MHz to
350kHz. Leaving the RSET pin open will set the
operating frequency to the default operating
frequency 1.35MHz.
Frequency vs. RSET
0
200
400
600
800
1000
1200
1400
0 50 100 150 200 250
FREQUENCY (kHz)
Series1
Selecting the Inductor
(Step-Down Applications, see Figure 3)
A 1µH to 47µH inductor with a DC current rating
of at least 25% percent higher than the
maximum load current is recommended for
most applications. For high efficiency, the
inductor’s DC resistance should be less than
200m. Refer to Table 2 for suggested surface
mount inductors. For most designs, the required
inductance value can be derived from the
following equation.
SWLIN
OUTINOUT
fIV
)VV(V
L
×Δ×
−×
=
Where I
L
is the inductor ripple current.
Choose the inductor ripple current to be 30% of
the maximum load current. The maximum
inductor peak current is calculated from:
2
I
II
L
LOAD)MAX(L
Δ
+=
Under light load conditions below 100mA, a
larger inductance is recommended for improved
efficiency.
Also note that the maximum recommended load
current is 2A if the duty cycle exceeds 35%.
Selecting the Input Capacitor
The input capacitor reduces the surge current
drawn from the input supply and the switching
noise from the device. The input capacitor
impedance at the switching frequency should
be less than the input source impedance to
prevent high frequency switching current from
passing through the input. Ceramic capacitors
with X5R or X7R dielectrics are highly
recommended because of their low ESR and
small temperature coefficients. For most
applications, a 4.7µF capacitor is sufficient.
Selecting the Output Capacitor
The output capacitor keeps the output voltage
ripple small and ensures feedback loop stable.
The output capacitor impedance should be low
at the switching frequency. Ceramic capacitors
with X5R or X7R dielectrics are recommended
for their low ESR characteristics. For most
applications, a 2.2µF ceramic capacitor is
sufficient.
PC Board Layout
The high current paths (VSS, VDD and SW)
should be placed very close to the device with
short, direct and wide traces. The input
capacitor needs to be as close as possible to
the VDD and VSS pins. The external feedback
resistors should be placed next to the FB pin.
Keep the switch node traces short and away
from the feedback network.
