MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED

MPQ2451 Rev 1.02

www.MonolithicPower.com

12

5/3/2013

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Table 2: Inductor Selection Guide

Part Number

Inductance (µH)

Max DCR (Ω) Current Rating (A)

Dimensions

L x W x H (mm

Wurth Electronics

7440430022

2.2

0.028

2.5

4.8x4.8x2.8

744043003

3.3

0.035

2.15

4.8x4.8x2.8

7447785004

4.7

0.078

2.4

5.9x6.2x3.2

TOKO

D63CB-#A916CY-2R0M

2.0

0.019

2.36

6.2x6.3x3.0

D62CB-#A916CY-3R3M

3.3

0.026

2.17

6.2x6.3x3.0

D62CB-#A916CY-4R7M

4.7

0.032

2.1

6.2x6.3x3.0

TDK

LTF5022T-2R2N3R2

2.2

0.04

3.2

5.2x5.0x2.2

LTF5022T-3R3N2R5

3.3

0.06

2.5

5.2x5.0x2.2

LTF5022T-4R7N2R0

4.7

0.081

2.0

5.2x5.0x2.2

COOPER BUSSMANN

SD25-2R2

2.2

0.031

2.8

5.2x5.2x2.5

SD25-3R3

3.3

0.038

2.21

5.2x5.2x2.5

SD25-4R7

4.7

0.047

1.83

5.2x5.2x2.5

The input capacitor (C1) can be electrolytic,

tantalum or ceramic. When using electrolytic or

tantalum capacitors, add a small, high quality

ceramic capacitor—for example, a 0.1μF—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:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

×

×

=

Δ

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:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

×

×

+

×

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

×

=

Δ

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

ΔV

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

ΔV

×

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

×

=

The characteristics of the output capacitor also

affect the stability of the regulation system.