MP2102 – 1.5MHz, 800mA DUAL-OUTPUT SYNCHRONOUS STEP-DOWN CONVERTER
MP2102 Rev. 1.1 www.MonolithicPower.com 10
9/21/2007 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
Input Capacitor Selection (C1)
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 X7R or X5R dielectrics are
highly recommended because of their low ESR
and small temperature coefficients. For most
applications, a 4.7µF capacitor is sufficient.
Output Capacitor Selection (C2, C3)
The output capacitor keeps output voltage
ripple small and ensures regulation loop
stability. The output capacitor impedance shall
be low at the switching frequency. Ceramic
capacitors with X5R or X7R dielectrics are
recommended. The output ripple V
OUT
is
approximately:
()
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
××
+×
××
−×
≤∆
OUTOSCOSCIN
OUTINOUT
OUT
Cf8
1
ESR
LfV
VVV
V
Where C
OUT
is C2 or C3.
Thermal Dissipation
Power dissipation shall be considered when
both channels of the MP2102 provide maximum
800mA output current to the loads at high
ambient temperature with low input supply
voltage. If the junction temperature rises above
150°C, the MP2102 two channels will be shut
down.
The junction-to-ambient thermal resistance of
the 10-pin QFN (3mm x 3mm) R
JA
is 50°C/W.
Therefore, the maximum power dissipation is
about 1.6W when the MP2102 is operating in a
70°C ambient temperature environment.
W6.1
W/C50
C70C150
PD
o
oo
MAX
=
−
=
PC Board Layout
The high current paths (GND, VIN and
SW1/SW2) should be placed very close to the
device with short, direct and wide traces. Input
capacitors should be placed as close as
possible to the VIN and GND pins. The external
feedback resistors shall be placed next to the
FB pins. Keep the switching nodes SW1/SW2
short and away from the feedback network.
