TM
MP2104 – 1.7MHz 600mA SYNCHRONOUS STEP-DOWN CONVERTER
PC Board Layout
Input Capacitor Selection
The input capacitor reduces the surge current
drawn from the input and switching noise from
the device. The input capacitor impedance at
the switching frequency shall be less than input
source impedance to prevent high frequency
switching current passing to 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.
The high current paths (GND, IN and SW)
should be placed very close to the device with
short, direct and wide traces. Input capacitor C1
needs to be as close as possible to the IN and
GND pins. The external feedback resistors shall
be placed next to the FB pin. Keep the
switching node SW short and away from the
feedback network. Figure 3 illustrates an
example of PCB layout and signal routing.
Output Capacitor Selection
The output capacitor keeps output voltage
ripple small and ensures regulation loop stable.
The output capacitor impedance shall be low at
the switching frequency. Ceramic capacitors
with X5R or X7R dielectrics are recommended.
The output ripple ∆VOUT is approximately:
⎛
⎜
⎝
⎞
⎟
⎟
⎠
VOUT
×
(
V
− VOUT
)
1
IN
⎜
Figure 3—MP2104 Suggested Layout
∆VOUT
≤
× ESR +
V × fOSC × L
8 × fOSC × C3
IN
For the fixed output versions (MP2104DJ-1.5
and MP2104-1.8), R1 is shorted and R2 is
open.
Efficiency vs
Load Current
100
V
= 3.3V
V
IN
90
80
70
60
50
40
30
20
10
0
OUTPUT
1.8V
600mA
4
3
5
INPUT
IN
SW
2.5V - 6V
= 4.2V
IN
MP2104
1
EN
FB
OFF ON
GND
2
MP2104_F04
10
100
LOAD CURRENT (mA)
1000
MP2104-EC02
Figure 4—VIN = 2.5V to 6V, VOUT = 1.8V, ILOAD = 600mA Step-Down Circuit
(L = 10µH for Higher Light-Load Efficiency)
NOTICE: MPS believes the information in this document to be accurate and reliable. However, it is subject to change without
notice. Contact MPS for current specifications. MPS encourages users of its products to ensure that third party Intellectual
Property rights are not infringed upon when integrating MPS products into any application. MPS cannot assume any legal
responsibility for any said applications.
MP2104 Rev. 1.0
10/4/05
© 2004 MPS, Inc.
Monolithic Power Systems, Inc.
983 University Avenue, Building A, Los Gatos, CA 95032 USA
Tel: 408-357-6600 ♦ Fax: 408-357-6601 ♦ www.MonolithicPower.com
9
MPS [ MONOLITHIC POWER SYSTEMS ]
