DC to DC Synchronous Converter Design

Abdus Sattar, IXYS Corporation

IXAN0068

11

The estimated efficiency,

%

93

93

.

0

6

.

42

6

.

39

=

=

=

η

%,

Estimated input current:

If we assume only 93% efficiency, then the estimated input current can be obtained,

Estimated input current,

η

•

=

Vin

VoIo

I

in

=

A

5

.

3

93

.

0

12

12

3

.

3

=

•

•

A

Bootstrap Circuit Design: [3]

Selecting bootstrap circuit components are done with consideration of the electrical rating

and characteristics of the high-side MOSFET (Q1).

The capacitance is defined by datasheet of IXS839 driver,

BST

total

G

BST

V

Q

C

Δ

=

)

(

(24)

VBST

Δ

is the

uF

mV

nC

C

BST

210

.

0

200

42

=

=

The bootstrap diode and capacitor voltage rating should be

DD

IN

pacitor

DiodeandCa

Bootstrap

V

V

V

+

>

_

The average forward current is defined by,

SW

total

G

Avg

F

f

Q

I

•

=

)

(

)

(

(25)

mA

5

.

10

10

250

10

42

3

9

=

•

•

•

=

−

Bibliography

[1] “Synchronous Buck MOSFETs loss calculation” AN-6005, Jon Klein, Fairchild

Semiconductor, 01/04/2006, www.fairchildsemi.com

[2] “Examination of reverse recovery losses in a synchronous buck converter circuit”

Application Note from Silicon Semiconductor, 2003, www.siliconsemi.com

[3] Datasheet for ISL6594D “Advanced Synchronous Rectified Buck MOSFET Driver”

from Intersil Corporation, 2007, www.intersil.com