MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER

MP1570 Rev. 1.5

www.MonolithicPower.com

9

1/31/2006

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TM

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 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 340KHz switching

frequency, or the following relationship is valid:

2

f

R

2

C

2

1

S

ESR

<

×

×

π

is the case, then add the second compensation

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.

MP1570

SW

BS

10nF

5V

MP1570_F02

Figure 2—External Bootstrap Diode

This diode is also recommended for high duty

cycle operation (when

IN

OUT

V

V

>65%) and high

TYPICAL APPLICATION CIRCUITS

INPUT

4.75V to 23V

OUTPUT

2.5V

3A

C3

3.3nF

C6

(optional)

D1

B130

(optional)

C5

10nF

MP1570

BS

IN

FB

SW

1

3

5

6

4

8

7

2

SS

GND

COMP

EN

MP1570_F03

Figure 3—MP1570 with AVX 47µF, 6.3V Ceramic Output Capacitor