MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER

MP2365 Rev. 0.91

www.MonolithicPower.com

9

7/10/2006

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© 2006 MPS. All Rights Reserved.

To optimize the compensation components for

conditions not listed in Table 3, the following

procedure can be used.

1. Choose the compensation resistor (R3) to set

the desired crossover frequency. Determine the

R3 value by the following equation:

FB

OUT

CS

EA

C

V

V

G

G

f

2

C

2

3

R

×

×

×

×

π

=

2. Choose the compensation capacitor (C3) to

achieve

the

desired

phase

margin.

For

applications with typical inductor values, setting

crossover frequency provides sufficient phase

margin. Determine the C3 value by the following

equation:

C

f

3

R

2

4

3

C

×

×

π

>

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 1.4MHz switching frequency, or 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 the

C6 value by the equation:

3

R

R

2

C

6

C

ESR

×

=

External Bootstrap Diode

It is recommended that an external bootstrap

diode be added when the system has a 5V

fixed input or the power supply generates a 5V

output. This helps improve the efficiency of the

regulator. The bootstrap diode can be a low

cost one such as IN4148 or BAT54.

MP2365

SW

BS

10nF

5V

Figure 2—External Bootstrap Diode

This diode is also recommended for high duty

cycle operation (when

IN

OUT

V

V

>65%) and high