MP2115 – 2A, 6V SYNCHRONOUS STEP-DOWN CONVERTER

MP2115 Rev. 1.0

www.MonolithicPower.com

9

2/28/2011

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© 2011 MPS. All Rights Reserved.

APPLICATION INFORMATION

Output Voltage Setting

The external resistor divider sets the output

voltage (see Typical Application Circuit on page

1). The feedback resistor (R1) also sets the

feedback loop bandwidth with the internal

compensation capacitor (see Figure 1-Function

Block Diagram).

Choose R1 around 500kΩ for optimal transient

response. R2 is then given by:

1

V

6

.

0

V

1

R

2

R

=

Table 2—Resistor Selection vs. Output

Voltage Setting

R1

R2

1.2V

51kΩ (1%)

51kΩ (1%)

1.5V

51kΩ (1%)

34kΩ (1%)

1.8V

51kΩ (1%)

25.5kΩ (1%)

2.5V

51kΩ (1%)

16kΩ (1%)

3.8V

51kΩ (1%)

9.53Ω(1%)

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 3 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

1

L

×

∆

×

−

×

=

inductor ripple current approximately 30% of the

maximum load current, 2.5A.

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 4 lists inductors recommended

for this purpose.

Table 3—Suggested Surface Mount Inductors

Manufacturer

Part Number

Inductance (µH)

Max DCR (Ω)

Saturation

Current (A)

Dimensions

LxWxH (mm

Coilcraft

D63CB

4.7

0.026

2

6.3X6.3X3.5

Toko

D53LC

4.7

0.026

2

6.3X6.3X3.5

Sumida

CDC5D23B

4.7

0.062

1.6

6.0X6.0X2.5

Table 4—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