MP1583 – 3A, 23V, 385KHz STEP-DOWN CONVERTER

MP1583 Rev. 3.1

www.MonolithicPower.com

9

6/20/2011

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To optimize the compensation components for

conditions not listed in Table 2, the following

procedure can be used.

1. Choose the compensation resistor (R3) to set

the desired crossover frequency. Determine R3

by the following equation:

FB

OUT

CS

EA

C

V

V

G

G

f

2

C

2

3

R

×

×

×

×

π

=

(which typically has a value no higher than

38KHz).

2. Choose the compensation capacitor (C3) to

achieve

the

desired

phase

margin.

For

applications with typical inductor values, setting

the crossover frequency provides sufficient

phase margin. Determine C3 by the following

equation:

C

f

3

R

2

4

3

C

×

×

π

>

Where R3 is the compensation resistor value.

3. Determine if the second compensation

capacitor (C6) is required. It is required if the

ESR zero of the output capacitor is located at

less than half of the 385KHz switching

frequency, or if the following relationship is valid:

2

f

R

2

C

2

1

S

ESR

<

×

×

π

If this is the case, then add the second

at the location of the ESR zero. Determine C6

by the equation:

3

R

R

2

C

6

C

ESR

×

=

PCB Layout Guide

PCB layout is very important to achieve stable

operation. Please follow these guidelines and

take Figure2 and 3 for references.

1) Keep the path of switching current short

and minimize the loop area formed by Input

cap, high-side and low-side MOSFETs.

2) Keep the connection of low-side MOSFET

between SW pin and input power ground

as short and wide as possible.

3) Ensure all feedback connections are short

and direct. Place the feedback resistors

and compensation components as close to

the chip as possible.

4) Route SW away from sensitive analog

areas such as FB.

5) Connect IN, SW, and especially GND

respectively to a large copper area to cool

the chip to improve thermal performance

and long-term reliability. For single layer,

do not solder exposed pad of the IC

C1

D1

R1

C2

R4

SGND

PGND

L1

C3

C6

R2

R3

SGND

Figure 2―PCB Layout (Single Layer)