TM
MP2109 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER
Table 2—Suggested Surface Mount Inductors
Manufacturer
Coilcraft
Toko
Sumida
Part Number
LP03310-222ML
1002AS
CDRH3D16
Inductance (µH)
2.2
2.2
2.2
Max DCR (Ω)
0.15
0.11
0.072
Saturation
Current (A)
1.1
1.14
1.20
Dimensions
LxWxH (mm
3
)
3.3 x 3.3 x 1
4.6 x 4.6 x 1.2
4 x 4 x 1.8
Table 3—Inductors for Improved Efficiency at 25mA, 50mA, under 100mA Load.
Manufacturer
Coilcraft
Murata
Sumida
Sumida
Part Number
DO1605T-103MX
LQH4C100K04
CR32-100
CR54-100
Inductance (µH)
10
10
10
10
Max DCR (Ω)
0.3
0.2
0.2
0.1
Saturation
Current (A)
1.0
1.2
1.0
1.2
I
RMS
(A)
0.9
0.8
0.7
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:
∆
V
OUT
≤
⎞
V
OUT
×
(
V
IN
−
V
OUT
)
⎛
1
⎟
× ⎜
ESR
+
⎜
V
IN
×
f
OSC
×
L
8
×
f
OSC
×
C3
⎟
⎠
⎝
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.
PD
MAX
=
150
o
C
−
70
o
C
50 C / W
o
=
1 .6 W
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.
MP2109 Rev.1.3
2/21/2006
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