MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER

MP1591 Rev. 2.1

www.MonolithicPower.com

8

12/5/2005

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2005 MPS. All Rights Reserved.

TM

To optimize the compensation components that

are not listed in Table 4, use the following

procedure.

Choose the compensation resistor to set the

desired crossover frequency. Determine the

value by the following equation:

REF

CS

EA

C

OUT

V

G

G

f

V

5

C

2

3

R

×

×

×

×

×

π

=

Putting in the know constants and setting the

crossover frequency to the desired 33KHz:

OUT

7

V

5

C

10

88

.

6

3

R

×

×

×

≅

Choose the compensation capacitor to set the

zero below one fourth of the crossover

frequency. Determine the value by the following

equation:

3

R

10

93

.

1

f

3

R

2

4

C

5

C

−

×

≈

×

×

π

>

Determine

if

the

second

compensation

capacitor, C3, is required. It is required if the

ESR zero of the output capacitor occurs at less

than four times the crossover frequency, or

1

f

R

5

C

8

C

ESR

≥

×

×

×

π

If this is the case, then add the second

compensation resistor. Determine the value by

the equation:

3

R

R

5

C

3

C

)

MAX

(

ESR

×

=

output capacitor.

Example:

Use the nearest standard value of 7.5kΩ.

Use standard value of 2.7nF.

Therefore, no second compensation capacitor

(C3) is required.

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.

MP1591

SW

BS

10nF

5V

MP1591_F02

Figure 2—External Bootstrap Diode

This diode is also recommended for high duty

cycle operation (when

IN

OUT

V

V

>65%) and high