MP2360 – 1.8A, 24V, 1.4MHz STEP-DOWN CONVERTER
MP2360 Rev. 0.91 www.MonolithicPower.com 6
5/19/2008 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2008 MPS. All Rights Reserved.
APPLICATION INFORMATION
Setting Output Voltage
The external resistor divider is used to set the
output voltage (see the schematic on front
page). The feedback resistor R1 also sets the
feedback loop bandwidth with the internal
compensation capacitor (see Figure 1). R2 can
be determined by:
1
V81.0
V
1R
2R
OUT
−
=
Table 1—Resistor Selection for Common
Output Voltages
V
OUT
(V) R1 (k) R2 (k)
1.8 80.6 (1%) 64.9 (1%)
2.5 49.9 (1%) 23.7 (1%)
3.3 49.9 (1%) 16.2 (1%)
5 49.9 (1%) 9.53 (1%)
Selecting the Inductor
A 1µH to 10µH inductor with a DC current rating
of at least 25% percent higher than the
maximum load current is recommended for
most applications. For highest efficiency, the
inductor’s DC resistance should be less than
200m. For most designs, the required
inductance value can be derived from the
following equation.
OSCLIN
OUTINOUT
fIV
)VV(V
L
×∆×
−×
=
Where I
L
is the inductor ripple current.
Choose an inductor with a rating current of
approximately 30% higher than the maximum
load current if the maximum load current is
1.8A. The maximum inductor peak current is
calculated from:
2
I
II
L
LOAD)MAX(L
∆
+=
Under light load conditions below 100mA, a
larger inductance is recommended for improved
efficiency. See Table 2 for suggested inductors.
Selecting the Input Capacitor
The input capacitor reduces the surge current
drawn from the input 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 10µF capacitor is sufficient.
Selecting the Output Capacitor
The output capacitor keeps output voltage ripple
small and ensures loop stability. 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
22µF ceramic capacitor will be sufficient.
PCB Layout Guide
PCB layout is very important to achieve stable
operation. Please follow these guidelines and
take Figure2 for references.
1) Keep the path of switching current short
and minimize the loop area formed by Input
cap, high-side MOSFET and schottky diode.
2) Keep the connection of schottky diode
between SW pin and input power ground
as short and wide as possible.
3) Ensure all feedback connections are short
and direct. Place the feedback resistors
and compensation components as close to
the chip as possible.
4) Route SW away from sensitive analog
areas such as FB.
5) Connect IN, SW, and especially GND
respectively to a large copper area to cool
the chip to improve thermal performance
and long-term reliability. For single layer,
do not solder exposed pad of the IC.
