MP2127 – 2.7-6V, 2A, 1.2MHZ SYNCHRONOUS STEP-DOWN CONVERTER

MP2127 Rev. 0.91

www.MonolithicPower.com

9

4/27/2010

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© 2010 MPS. All Rights Reserved.

APPLICATION INFORMATION

Output Voltage Setting

The output voltage is set by the external resistor

divider:

)

1

(

8

.

0

2

1

R

R

V

OUT

+

⋅

=

The divider ratio also affects the loop bandwidth of

the

step-down

converter.

The

approximate

relationship between them is given below:

)

1

(

240

1

2

1

1

R

R

k

R

BW

+

⋅

+

∝

To minimize the impact of R1 to loop bandwidth,

one should choose R1 much smaller than 240k.

Some recommended value for common output

voltage is listed below:

Table 1—Resistor Selection vs. Output

Voltage Setting

R1

R2

1.2V

20kΩ (1%)

40.2kΩ (1%)

1.8V

49.9kΩ (1%) 40.2kΩ (1%)

2.5V

84.5kΩ (1%) 40.2kΩ (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 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

×

Δ

×

−

×

=

inductor ripple current approximately 30% of the

maximum load current, 2A.

The maximum inductor peak current is:

2

I

I

I

L

LOAD

)

MAX

(

L

Δ

+

=

Table 2—Suggested Inductors

Manufacturer Part Number

Inductance

(μH)

Dimensions

LxWxH

(mm

TOKO

B1015AS-

3R0N

3

8.4X8.3X4

TDK

RLF7030T-

3R3M4R1

3.3

7.3X6.8X3.2

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 10μF capacitor is sufficient.

Output Capacitor COUT 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. For

forced PWM mode operation, the output ripple

)

1

8

1

(

)

(

OUT

OSC

ESR

OSC

IN

OUT

IN

OUT

OUT

C

f

R

L

f

V

V

V

V

V

⋅

⋅

+

⋅

⋅

−

⋅

=

Δ

F

or most applications, a 33μF capacitor is

sufficient.

Thermal Dissipation

Power dissipation shall be considered when

operates MP2127 at maximum 2A output current.

If the junction temperature rises above 150

°C,

MP2127 will be shut down by internal thermal

protection circuitry.