MP1580HS-LF-Z データシートの表示（PDF） - Monolithic Power Systems

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MP1580HS-LF-Z

2A, 380 KHz Step-Down Converter

Monolithic Power Systems 

TM

MP1580 – 2A, 380KHz STEP-DOWN CONVERTER

Input Capacitor

The input current to the step-down converter is

discontinuous, so a capacitor is required to

supply the AC current to the step-down

converter while maintaining the DC input

voltage. A low ESR capacitor is required to

keep the noise at the IC to a minimum. Ceramic

capacitors are preferred, but tantalum or low-

ESR electrolytic capacitors will also suffice.

The input capacitor value should be greater

than 10µF. The capacitor can be electrolytic,

tantalum or ceramic. However, since it absorbs

the input switching current it requires an

adequate ripple current rating. Its RMS current

rating should be greater than approximately 1/2

of the DC load current.

To ensure stable operation, C1 should be

placed as close to the IN pin as possible.

Alternately, a smaller high quality ceramic

0.1µF capacitor may be placed closer to the IN

pin and a larger capacitor placed further away.

If using this technique, it is recommended that

the larger capacitor be a tantalum or electrolytic

type capacitor. All ceramic capacitors should be

placed close to the MP1580.

Output Capacitor

The output capacitor is required to maintain the

DC output voltage. Low ESR capacitors are

preferred to keep the output voltage ripple low.

The characteristics of the output capacitor also

affect the stability of the regulation control

system. Ceramic, tantalum or low ESR

electrolytic capacitors are recommended. In the

case of ceramic capacitors, the impedance at

the oscillator frequency is dominated by the

capacitance, so the output voltage ripple is

mostly independent of the ESR. The output

voltage ripple is estimated to be:

VRIPPLE

≅ 1.4 × VIN

×

⎜⎜⎝⎛

fLC

f

⎟⎟⎠⎞ 2

Where VRIPPLE is the output ripple voltage, fLC is

the resonant frequency of the LC filter and f is

the oscillator frequency.

In the case of tantalum or low-ESR electrolytic

capacitors, the ESR dominates the impedance

at the oscillator frequency, therefore the output

ripple is calculated as:

VRIPPLE ≅ ∆I × RESR

Where VRIPPLE is the output voltage ripple and

RESR is the equivalent series resistance of the

output capacitors.

Output Rectifier Diode

The output rectifier diode supplies the current to

the inductor when the upper transistor M1 is off.

To reduce losses due to the diode forward

voltage and recovery times, use a Schottky

rectifier.

Table 2 provides the Schottky rectifier part

numbers based on the maximum input voltage

and current rating.

Table 2—Schottky Rectifier Selection Guide

VIN (Max)

15V

20V

26V

2A Load Current

Part Number

Vendor

30BQ015

4

B220

1

SK23

6

SR22

6

20BQ030

4

B230

1

SK23

6

SR23

3, 6

SS23

2, 3

Table 3 lists some rectifier manufacturers.

Table 3—Schottky Diode Manufacturers

Vendor

Web Site

Diodes, Inc.

www.diodes.com

Fairchild Semiconductor www.fairchildsemi.com

General Semiconductor www.gensemi.com

International Rectifier www.irf.com

On Semiconductor

www.onsemi.com

Pan Jit International

www.panjit.com.tw

Choose a rectifier that has a maximum reverse

voltage rating greater than the maximum input

voltage, and a current rating greater than the

maximum load current.

MP1580 Rev. 3.0

www.MonolithicPower.com

6

12/5/2005

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© 2005 MPS. All Rights Reserved.

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