MP2209 – 16V, 2A, 600KHz SYNCHRONOUS STEP-DOWN CONVERTER

MP2209 Rev. 1.01

www.MonolithicPower.com

10

7/11/2013

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APPLICATION INFORMATION

Setting the Output Voltage

The external resistor divider sets the output

voltage (see Figure 1). The feedback resistor R1

also sets the feedback loop bandwidth with the

internal compensation network (see Figure 1).

The relation between R1 and feedback loop

follows:

6

CO

1.24 10

R1(K )

f(KHz) C (uF)

×

Ω=

×

it’s usually set to be in the range of 30KHz and

50KHz for optimal transient performance and

good phase margin. If electrolytic capacitor is

used, the recommended loop bandwidth is no

ESR

ESR

O

1

f

2R

C

=

π×

×

523KΩ. R2 is then given by:

OUT

R1

R2

V

1

0.8V

=

−

Table 1—Resistor Selection vs. Output

Voltage Setting

VOUT

(V)

R1

(kΩ)

R2

(kΩ)

L (μH)

COUT

(ceramic)

1.2

499

1000

1μH-4.7μH

47μF

1.5

499

562

1μH-4.7μH

47μF

1.8

499

402

1μH-4.7μH

47μF

3.3

499

158

1μH-4.7μH

47μF

5

499

95.3

1μH-4.7μH

47μF

Table 2—Suggested Surface Mount Inductors

Manufacturer

Part Number

Inductance

(μH)

Max

DCR

(mΩ)

Current

Rating (A)

Dimensions L x W x

H (mm3)

TOKO

FDA1055-3R3M

3.3

7.3

11.7

10.8x11.6x5.5

Wurth Electronics

744314330

3.3

9.6

8

7x6.9x5

TDK

ULF100457-3R3N6R9

3.3

11.6

7.5

10x9.7x4.5

Selecting the Inductor

A 1μH to 4.7μH 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

<10mΩ. See Table 2 for recommended inductors

and manufacturers. For most designs, the

inductance value can be derived from the

following equation:

OUT

IN

OUT

IN

L

OSC

Vx(V

V

)

L

Vx I xf

−

=

Δ

inductor ripple current approximately 30% of the

maximum load current, 2A. The maximum

inductor peak current is

L

L(MAX)

LOAD

I

II

2

Δ

=+

Under light load conditions, larger inductance is

recommended for improved efficiency

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 47μF capacitor is sufficient.