MP1580 – 2A, 380KHz STEP-DOWN CONVERTER

MP1580 Rev. 3.0

www.MonolithicPower.com

8

12/5/2005

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© 2005 MPS. All Rights Reserved.

TM

Determine

if

the

second

compensation

capacitor, C6, is required. It is required if the

ESR zero of the output capacitor happens at

less than four times the crossover frequency.

Or:

1

f

R

2

C

8

C

ESR

≥

×

×

×

π

or

1

V

R

3

R

10

34

.

7

OUT

ESR

5

≥

×

×

×

−

If

this

is

the

case,

add

the

second

compensation capacitor. Determine the value

by the equation:

3

R

R

2

C

6

C

)

MAX

(

ESR

×

=

output capacitor.

For example:

C2= 22µF Ceramic (ESR = 10mΩ)

Ω

=

×

×

×

×

≈

−

k

9

.

9

)

3

.

3

(

)

10

22

(

)

10

37

.

1

(

3

R

6

8

Use the nearest standard value of 10kΩ.

nF

6

.

1

10

10

3

.

3

)

10

22

(

22

.

0

3

C

3

6

=

×

×

×

×

>

−

Use a standard value of 2nF

014

.

0

f

R

2

C

2

C

ESR

=

×

×

×

π

which is less than 1, therefore no second

compensation capacitor is required.

Table 5—Recommended Components for

Standard Output Voltages

R1

L1 Minimum

1.22V

0Ω

6.8µH

1.5V

2.32kΩ

6.8µH

1.8V

4.75kΩ

10µH

2.5V

10.5kΩ

10µH

3.3V

16.9kΩ

15µH

5.0V

30.9kΩ

22µH

Negative Output Voltage

The MP1580 can be configured as a buck-

boost regulator to supply negative output

voltage.

Because the GND pin of the IC is now

connected to the negative output voltage, the

maximum allowable input voltage is the IC input

voltage rating (25V) minus the negative output

voltage value. A typical application circuit is

shown in Figure 3.

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.

MP1580

SW

BS

10nF

5V

MP1580_F02

Figure 2—External Bootstrap Diode

This diode is also recommended for high duty

cycle operation (when

IN

OUT

V

V

>65%) and high