ACT411

Rev 4, 27-Feb-14

- 11 -

www.active-semi.com

Copyright © 2014 Active-Semi, Inc.

Active-Semi Proprietary―For Authorized Recipients and Customers

ActivePSR

TYPICAL APPLICATION CONT’D

An EE16 core is selected for the transformer. From

the manufacture’s catalogue recommendation, the

is:

The turns of secondary and auxiliary winding can

be derived accordingly:

Determining the value of the current sense resistor

(R9) uses the peak current in the design. Since the

ACT411 internal current limit is set to 1V, the

design of the current sense resistor is given by:

The voltage feedback resistors are selected

according to the Ioccmax and Vo. The design

Io_cc max is given by:

The design Vo is given by:

Where k is IC constant and K=0.000075, then we

can get the value:

When selecting the output capacitor, a low ESR

electrolytic capacitor is recommended to minimize

ripple from the current ripple. The approximate

equation for the output capacitance value is given

by:

Two 470µF electrolytic capacitors are used to keep

the ripple small.

PCB Layout Guideline

Good PCB layout is critical to have optimal

performance. Decoupling capacitor (C4) and

feedback resistor (R5/R6) should be placed close to

VDD and FB pin respectively. There are two main

power path loops. One is formed by C1/C2, primary

winding, Mosfet transistor and current sense

resistor (R9). The other is secondary winding,

rectifier D8 and output capacitors (C5/C6). Keep

these loop areas as small as possible. Connecting

high current ground returns, the input capacitor

ground lead, and the ACT411 GND pin to a single

point (star ground configuration).

T

78

T

/

nH

65

mH

4

.

0

A

L

N

2

LE

P

P

=

=

=

(13)

T

13

78

18

.

5

1

N

N

N

N

p

p

s

S

≈

×

=

×

=

(14)

T

14

13

08

.

1

N

N

N

N

s

S

A

A

=

×

=

×

=

(15)

Ω

η

.

24

.

1

85

.

0

kHz

110

mH

4

.

0

12

6

.

1

2

1

F

L

V

I

2

V

R

system

SW

P

OUT

OCP

_

OUT

CS

CS

≈

×

×

×

×

=

×

×

×

×

=

(16)

(17)

D

FB

a

s

2

fb

1

fb

o

V

V

N

N

)

R

R

1

(

V

−

×

×

+

=

(18)

K

2

.

10

R

,

K

6

.

53

R

2

fb

1

fb

=

=

(19)

F

182

mV

50

k

110

1

V

f

I

C

RIPPLE

sw

OUT

OUT

μ

=

×

=

×

=

(20)

sw

_

f

cs

cs

p

D

O

2

fb

1

fb

2

fb

1

fb

s

p

s

K

R

V

L

V

V

R

R

R

R

N

N

f

×

×

+

×

+

×

×

=