MP2101 – 1.6MHz SYNCHRONOUS STEP-DOWN PLUS 200mA LDO

MP2101 Rev. 1.0

www.MonolithicPower.com

9

8/18/2006

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© 2006 MPS. All Rights Reserved.

TM

APPLICATION INFORMATION

Output Voltage Setting

The external resistor divider sets the output

voltage. The feedback resistor R1 of the switcher

also sets the feedback loop bandwidth with the

internal compensation capacitor (see Figure 1).

R1 of the switcher should be 300kΩ for optimal

transient response. R2 is then given by:

1

V

6

.

0

V

1

R

2

R

1

OUT

−

=

R4 of the LDO should be 60kΩ for good loop

response. R3 is then given by:

)

1

V

6

.

0

V

(

4

R

3

R

2

OUT

−

×

=

Table 1—Resistor Selection vs. Output

Voltage Setting

R1

R2

R3

R4

1.2V

300k

Ω

(1%)

300k

Ω

(1%)

60kΩ

(1%)

60kΩ

(1%)

1.5V

300k

Ω

(1%)

200k

Ω

(1%)

90kΩ

(1%)

60kΩ

(1%)

1.8V

300k

Ω

(1%)

150k

Ω

(1%)

120kΩ

(1%)

60kΩ

(1%)

2.5V

300k

Ω

(1%)

95.3k

Ω

(1%)

190kΩ

(1%)

60kΩ

(1%)

Inductor Selection

A 1µH to 10µH inductor with a DC current rating

of at least 25% higher than the maximum load

current is recommended for most applications.

For best efficiency, the inductor DC resistance

should

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

×

∆

×

−

×

=

Choose the inductor ripple current to be

approximately 30% of the maximum load

current (800mA).

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

Sumida

CDRH2D11

2.2

0.098

1.27

3.2 x 3.2 x 1.2

Toko

D521C

2.2

0.059

1.63

5 x 5 x 1.5

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