AP1695

Document number: DS37312 Rev. 1 - 2

9 of 15

www.diodes.com

June 2014

© Diodes Incorporated

AP1695

A Product Line of

Diodes Incorporated

Design Parameters

Setting the Current Sense Resistor R8

According to the equation of the output current, the current sense resistor R8 is determined:

_

_

8

cs ref

o mean

V

Rk

I







Transformer Selection

The typical non-isolated buck circuit in Figure 1 is usually selected, and the system is operating at boundary conduction mode. The switching

_

_

_

min

( 2

)

8

2

in rms

o

o

cs ref

in rms

V

V

R V

L

V

V

f

















Where,

o

_

in rms

V

is the RMS value of the input voltage.

_

8

pk

cs ref

L

e

m

e

m

L i

L V

N

A B

A B

R











Where,

e

m

cc

aux

L

od

V

NN

VV





Where,

Setting the Initial On Time

As the AP1695 adopts constant on time control method, the AP1695 will generate an initial on time to start a working cycle. If the initial on time is

longer than the rated on time, overshoot will happen. The initial on time is determined by resister R1 shown in Figure 1.

s

R

t

initial

on

12

_

10

1

80









To guarantee the system with no overshoot phenomenon, the resistor R1 is selected: