MP2354 – 2A, 23V, 380KHz STEP-DOWN CONVERTER

MP2354 Rev. 1.4

www.MonolithicPower.com

8

1/6/2006

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TM

MP2354 can be optimized for a wide range of

capacitance and ESR values.

Output Rectifier Diode

The output rectifier diode supplies the current to

the inductor when the upper transistor M1 is off.

Use a Schottky diode to reduce losses due to

the diode forward voltage and recovery times.

Choose a diode whose maximum reverse

voltage rating is greater than the maximum

input voltage, and whose current rating is

greater than the maximum load current.

Table 2 provides the Schottky diode part

numbers based on the maximum input voltage

and current rating.

Table 2—Schottky Rectifier Selection Guide

2A Load Current

Part Number

Vendor

(5)

15V

30BQ015

4

B220

1

SK23

6

20V

SR22

6

20BQ030

4

B230

1

SK23

6

SR23

3, 6

26V

SS23

2, 3

Note:

5) Refer to Table 3 for Rectifier Manufacturers

Table 3—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

Compensation

MP2354 employs current mode control for easy

compensation and fast transient response. The

system stability and transient response are

controlled through the COMP pin. COMP pin 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 gain of the voltage feedback loop is

given by:

OUT

FB

VEA

CS

LOAD

VDC

V

V

A

G

R

A

×

×

×

=

400V/V;

is

the

current

sense

resistor value.

The system has two poles of importance. One

is due to the compensation capacitor (C3) and

the output resistor of error amplifier, and the

other is due to the output capacitor and the load

resistor. These poles are located at:

VEA

EA

1

P

A

3

C

2

G

f

×

×

π

=

LOAD

2

P

R

2

C

2

1

f

×

×

π

=

Where

is

the

error

amplifier

transconductance, 770µA/V.

The system has one zero of importance, due to

the compensation capacitor (C3) and the

compensation resistor (R3). This zero is located

at:

3

R

3

C

2

1

Z

×

×

π

=

longer transient settling time. A trade-off has to

be made between the stability and the transient

response. A typical value is less than one-fourth

of the crossover frequency.

The system may have another zero of

importance, if the output capacitor has a large

capacitance and/or a high ESR value. The zero,

due to the ESR and capacitance of the output

capacitor, is located at:

ESR

ESR

R

2

C

2

1

f

×

×

π

=