MP2104 – 1.7MHz 600mA SYNCHRONOUS STEP-DOWN CONVERTER

MP2104 Rev. 1.3

www.MonolithicPower.com

8

10/4/2005

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TM

APPLICATION INFORMATION

Output Voltage Setting (MP2104DJ)

The external resistor divider sets the output

voltage (see Figure 3). The feedback resistor R1

also sets the feedback loop bandwidth with the

internal compensation capacitor (see Figure 1).

Choose R1 around 300kΩ for optimal transient

response. R2 is then given by:

1

V

6

.

0

V

1

R

2

R

=

Table 1—Resistor Selection vs. Output

Voltage Setting

R1

R2

1.2V

300k

300k

1.5V

300k

200k

1.8V

300k

150k

2.5V

300k

95.3k

Inductor Selection

A 1µH to 10µH inductor with DC current rating

at least 25% higher than the maximum load

current is recommended for most applications.

For best efficiency, the inductor DC resistance

shall

be

<200mΩ.

See

Table

2

for

recommended inductors and manufacturers.

For most designs, the inductance value can be

derived from the following equation:

()

OSC

L

IN

OUT

IN

OUT

f

I

V

V

V

V

L

×

∆

×

−

×

=

inductor ripple current approximately 30% of the

maximum load current, 600mA.

The maximum inductor peak current is:

2

I

I

I

L

LOAD

)

MAX

(

L

∆

+

=

Under light load conditions below 100mA, larger

inductance is recommended for improved

efficiency. Table 3 lists inductors recommended

for this purpose.

Table 2—Suggested Surface Mount Inductors

Manufacturer

Part Number

Inductance (µH)

Max DCR (Ω)

Saturation

Current (A)

Dimensions

LxWxH (mm

Coilcraft

LP1704-222M

2.2

0.07

1.7

6.5x5.3x2

Toko

D312C

2.2

0.14

1.0

3.6x3.6x1

Sumida

CDRH3D16

2.2

0.072

1.2

4x4x1.8

Taiyo Yuden

LBC2518

2.2

0.13

0.6

2.5x1.8x1.8

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

CMD4D06-100

10

0.3

0.7

0.5

Sumida

CR32-100

10

0.2

1.0

0.7

Sumida

CR54-100

10

0.1

1.2

1.4