MP2105 – 1MHz 800mA SYNCHRONOUS STEP-DOWN CONVERTER

MP2105 Rev. 1.2

www.MonolithicPower.com

7

8/19/2005

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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

D01605T-472

4.7

0.150

1.20

5.4x4.2x1.8

Toko

D52LC

4.7

0.087

1.14

5x5x2

Sumida

CR43-4R7

4.7

0.109

1.15

4.3x4.8x3.5

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

PC Board Layout

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 2 illustrates an

example of PCB layout and signal routing.

Figure 2—MP2105 Suggested Layout