MP2452―1A, 36V, 1MHz, STEP-DOWN CONVERTER

MP2452 Rev. 1.0

www.MonolithicPower.com

12

9/27/2010

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2010 MPS. All Rights Reserved.

Table 2—Inductor Selection Guide

Part Number

Inductance (µH)

Max DCR (Ω) Current Rating (A)

Dimensions

L x W x H (mm

Wurth Electronics

744062003

3.3

0.032

2.8

6.8x6.8x2.3

7447789004

4.7

0.035

2.9

7.3x7.3x3.2

7447789006

6.8

0.044

2.5

7.3x7.3x3.2

744065100

10

0.053

3

10x10x2.8

744066150

15

0.05

3.2

10x10x3.8

TOKO

D73CB-#636CY-3R3M

3.3

0.035

2.26

7.6x7.6x3.5

DS75LC-B1047AS -4R7N

4.7

0.026

3.5

7.6x7.6x5.0

DS75LC-B1047AS-6R8N

6.8

0.036

2.9

7.6x7.6x5.0

DS75LC-B1047AS -100M

10

0.053

2.3

7.6x7.6x5.0

DS85LC-B1000AS-150M

15

0.077

2.1

8.4x8.3x5.0

Input Capacitor

The input capacitor (C1) can be electrolytic,

tantalum or ceramic. When using electrolytic or

tantalum capacitors, a small, high quality ceramic

capacitor, i.e. 0.1µF, should be placed as close

to the IC as possible. When using ceramic

capacitors, make sure that they have enough

capacitance to provide sufficient charge to

prevent excessive voltage ripple at input. The

input voltage ripple caused by capacitance can

be estimated by:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

×

×

=

∆

IN

OUT

IN

OUT

S

LOAD

IN

V

V

1

V

V

1

C

f

I

V

Output Capacitor

The output capacitor (C2) is required to maintain

the DC output voltage. Ceramic, tantalum, or low

ESR electrolytic capacitors are recommended.

Low ESR capacitors are preferred to keep the

output voltage ripple low. The output voltage

ripple can be estimated by:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

×

×

+

×

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

×

=

∆

2

C

f

8

1

R

V

V

1

L

f

V

V

S

ESR

IN

OUT

S

OUT

OUT

equivalent series resistance (ESR) value of the

output capacitor.

In the case of ceramic capacitors, the impedance

at the switching frequency is dominated by the

capacitance. The output voltage ripple is mainly

caused by the capacitance. For simplification, the

output voltage ripple can be estimated by:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

×

×

×

=

IN

OUT

2

S

OUT

OUT

V

V

1

2

C

L

f

8

V

∆V

In the case of tantalum or electrolytic capacitors,

the ESR dominates the impedance at the

switching frequency. For simplification, the output

ripple can be approximated to:

ESR

IN

OUT

S

OUT

OUT

R

V

V

1

L

f

V

∆V

×

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

×

=

The characteristics of the output capacitor also

affect the stability of the regulation system.