MP2109 – DUAL 1.2MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER

MP2109 Rev.1.3

www.MonolithicPower.com

7

2/21/2006

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TM

Table 2—Suggested Surface Mount Inductors

Manufacturer

Part Number

Inductance (µH)

Max DCR (Ω)

Saturation

Current (A)

Dimensions

LxWxH (mm

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)

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.

()

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

×

×

+

×

×

×

−

×

≤

∆

3

C

f

8

1

ESR

L

f

V

V

V

V

V

OSC

OSC

IN

OUT

IN

OUT

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 maximum power dissipation is about 1.6W

when the MP2109 is operating in a 70

°C

ambient temperature environment.

W

6

.

1

W

/

C

50

C

70

C

150

PD

o

o

o

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.