f

D1

S1

D2

S2

SW 1

IN

SW

I

t

I

t

P

V

6

2

æ

ö

´

´

æ

ö æ

ö

=

´

+

´

ç

÷

ç

÷ ç

÷

è

ø è

ø

è

ø

(11)

D1

O UT

RIP P LE

D 2

O UT

RIP P LE

1

1

I

I

I

and

I

I

I

2

2

=

-

´

=

+

´

(12)

HFET _ Loss

COND1

SW1

P

P

P

=

+

(13)

(

)

(

)

2

2

I

RIPPLE

I

1 - D

I

RMS2

OUT

12

æ

ö

ç

÷

=

´

+

ç

÷

ç

÷

è

ø

(14)

(

)

( )

2

COND2

RMS2

DS ON 2

P

I

R

=

´

(15)

COND3

OUT

F

D

SW

P

I

V

t

=

´

´

´ f

(16)

RR

RR

IN

SW

1

P

Q

V

2

=

´

´

´ f

(17)

SR _ Loss

COND2

COND3

RR

P

P

P

P

=

+

+

(18)

TPS51113, TPS51163

Also, the switching loss can be approximately described as

where

• I

where

• t

• t

Therefore, the total power loss of the high-side MOSFET is estimated by the sum of the above power losses,

Synchronous Rectifier MOSFET Power Loss

body diode conduction loss and reverse recovery loss.

ה

, where T is the duration of one

switching cycle, the RMS current of the SR MOSFET can be calculated as follows.

The symchronous rectifier (SR) MOSFET conduction loss is

The body diode conduction loss is

where

• V

• t

The body diode recovery time – the time it takes for the body diode to restore its blocking capability from forward

conduction state, determines the reverse recovery losses.

where

• Q

Therefore, the total power loss of the SR MOSFET is estimated by the sum of the above power losses.

Copyright © 2009, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Link(s) :TPS51113 TPS51163