MP2212 – 16V, 3A, 600kHz SYNCHRONOUS STEP-DOWN CONVERTER

MP2212 Rev. 1.01

www.MonolithicPower.com

9

2/22/2012

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© 2012 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The external resistor divider sets the output

voltage (see Figure 1). For typical applications,

choose R2 to be 10k Ω. R1 is then given by:

OUT

V

R1 R2 (

1)

0.8V

=×

−

Table 1—Resistor Selection vs. Output

Voltage Setting

L (μH)

(ceramic)

1.2

5

10

1μH-4.7μH

47μF

1.5

8.75

10

1μH-4.7μH

47μF

1.8

12.5

10

1μH-4.7μH

47μF

2.5

21.25

10

1μH-4.7μH

47μF

3.3

31.25

10

1μH-4.7μH

47μF

Feed-forward capacitor

adding a feed-forward capacitor in parallel with

the feedback resistor from output to FB pin can

increase loop bandwidth, help reducing transient

overshoot and undershoot and startup overshoot

circuit with a 390pF feed-forward capacitor.

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,

3A.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.

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