MP1583 查看數據表（PDF） - Monolithic Power Systems

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MP1583

3A, 23V Step Down Converter

Monolithic Power Systems 

Monolithic Power Systems

Where VRIPPLE is the output ripple voltage, VIN

is the input voltage, fLC is the resonant

frequency of the LC filter, fSW is the switching

frequency. In the case of tanatalum or low-

ESR electrolytic capacitors, the ESR

dominates the impedance at the switching

frequency, and so the output ripple is

calculated as:

VRIPPLE ~= ∆I * RESR

Where VRIPPLE is the output voltage ripple, ∆I is

the inductor ripple current, 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 high-side switch is off.

To reduce losses due to the diode forward

voltage and recovery times, use a Schottky

rectifier.

Tables 3 provides the Schottky rectifier part

numbers based on the maximum input voltage

and current rating.

Table 3: Schottky Rectifier Selection Guide

VIN

(Max)

15V

20V

26V

2A Load Current

Part

Number

Vendor

30BQ15 4

B220

1

SK23

6

SR22

6

20BQ030 4

B230

1

SK23

6

SR23

3, 6

SS23

2, 3

3A Load Current

Part

Number

Vendor

B320

1

SK33

1, 6

SS32

3

B330

1

B340L

1

MBRD330 4, 5

SK33

1, 6

SS33

2, 3

Table 4 lists some rectifier manufacturers.

Table 4: Schottky Diode Manufacturers

# Vendor

Web Site

1 Diodes, Inc.

www.diodes.com

2 Fairchild Semiconductor www.fairchildsemi.com

3 General Semiconductor www.gensemi.com

4 International Rectifier www.irf.com

5 On Semiconductor

www.onsemi.com

6 Pan Jit International

www.panjit.com.tw

MP1583

3A, 23V

Step Down Converter

Choose a rectifier who’s maximum reverse

voltage rating is greater than the maximum

input voltage, and who’s current rating is

greater than the maximum load current.

Compensation

The system stability is controlled through the

COMP pin. COMP is the output of the internal

transconductance error amplifier. A series

capacitor-resistor combination sets a pole-zero

combination to control the characteristics of

the control system.

The DC loop gain is:

AVDC = (VFB / VOUT) * AVEA * GCS * RLOAD

Where:

• VFB is the feedback threshold voltage,

1.222V

• VOUT is the desired output regulation

voltage

• AVEA is the transconductance error amplifier

voltage gain, 400 V/V

• GCS is the current sense gain, (roughly the

output current divided by the voltage at

COMP), 3.8 A/V

• RLOAD is the load resistance (VOUT / IOUT

where IOUT is the output load current)

The system has 2 poles of importance, one is

due to the compensation capacitor (C3), and

the other is due to the output capacitor (C2).

These are:

fP1 = GMEA / (2π*AVEA*C3)

Where P1 is the first pole, and GMEA is the

error amplifier transconductance (800µS).

and

fP2 = 1 / (2π*RLOAD *C2)

MP1583 Rev 2.0_06/30/04

www.monolithicpower.com

6

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