MP2109 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER
MP2109 Rev.1.4 www.MonolithicPower.com 7
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Table 2—Suggested Surface Mount Inductors
Manufacturer Part Number Inductance (µH) Max DCR (Ω)
Saturation
Current (A)
Dimensions
LxWxH (mm
3
)
Coilcraft LP03310-222ML 2.2 0.15 1.1 3.3 x 3.3 x 1
Toko 1002AS 2.2 0.11 1.14 4.6 x 4.6 x 1.2
Sumida CDRH3D16 2.2 0.072 1.20 4 x 4 x 1.8
Table 3—Inductors for Improved Efficiency at 25mA, 50mA, under 100mA Load.
Manufacturer Part Number Inductance (µH) Max DCR (Ω)
Saturation
Current (A)
I
RMS
(A)
Coilcraft DO1605T-103MX 10 0.3 1.0 0.9
Murata LQH4C100K04 10 0.2 1.2 0.8
Sumida CR32-100 10 0.2 1.0 0.7
Sumida CR54-100 10 0.1 1.2 1.4
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.
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 ∆V
OUT
is approximately:
()
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
××
+×
××
−×
≤∆
3Cf8
1
ESR
LfV
VVV
V
OSCOSCIN
OUTINOUT
OUT
Thermal Dissipation
Power dissipation shall be considered when
both channels of the MP2109 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 MP2109 two channels will be shut
down.
The junction-to-ambient thermal resistance of
the 10-pin QFN (3mm x 3mm) R
ΘJA
is 50°C/W.
The maximum power dissipation is about 1.6W
when the MP2109 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 (GND1/GND2, IN1/IN2
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 respective IN 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.
