ACT410

Rev 3, 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 EFD15 core is selected for the transformer.

From

th e

manufacture’s

catalog u e

recommendation, the gapped core with an effective

the primary winding 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

ACT410 internal current limit is set to 1V, the

design of the current sense resistor is given by:

Where Fsw is the frequency at 4.75V CC mode.

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 820µF 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 D4 and output capacitors (C7/C6). Keep

these loop areas as small as possible. Connecting

high current ground returns, the input capacitor

ground lead, and the ACT410 GND pin to a single

point (star ground configuration).

T

76

T

/

nH

64

mH

37

.

0

A

L

N

2

LE

P

P

=

=

=

(13)

T

7

76

32

.

11

1

N

N

N

N

p

p

s

S

≈

×

=

×

=

(14)

T

20

7

28

.

2

N

N

N

N

s

S

A

A

≈

×

=

×

=

(15)

Ω

η

.

07

.

1

75

.

0

kHz

100

mH

37

.

0

5

6

.

2

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

5

.

11

R

,

K

68

R

2

fb

1

fb

=

=

(19)

F

364

mV

50

k

110

2

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

×

×

+

×

+

×

×

=