ZXLD1374

ZXLD1374

Document number: DS35032 Rev. 1 - 2

Page 17 of 35

www.diodes.com

October 2010

© Diodes Incorporated

A Product Line of

Diodes Incorporated

23

.

0

)

R

(R

R

V

V

I

I

2

GI

1

GI

1

GI

ADJ

GI

RS

LED

≈

+

=

=

Ω

=

−

=

k

110

)

1

V

V

(

R

R

GI

ADJ

1

GI

2

GI

This will result in:

Ω

=

+

=

m

150

I

mV

225

)

R

(R

R

R

LED

2

GI

1

GI

1

GI

s

Table 1

RGI1

RGI2

0.2

30k

Ω

120k

Ω

0.25

33k

Ω

100k

Ω

0.3

39k

Ω

91k

Ω

0.35

30k

Ω

56k

Ω

0.4

100k

Ω

150k

Ω

0.45

51k

Ω

62k

Ω

0.5

30k

Ω

30k

Ω

The values shown have been chosen so that they do not load REF too much or create offset errors due to the GI pin input

current. A ZXLD1374 calculator is available from http://www.diodes.com/destools/calculators.html that will help with

component selection.

INDUCTOR/FREQUENCY SELECTION

Recommended inductor values for the ZXLD1374 are in the range 22 µH to 100 µH.

The chosen coil should have a

saturation current higher than the peak sensed current and a continuous current rating above the required mean sensed

current by at least 50%.

The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the recommended

limits over the supply voltage and load current range.

The frequency compensation mechanism inside the chip tends to keep the frequency within the range 300kHz ~ 400kHz in

most of the operating conditions. Nonetheless, the controller allows for higher frequencies when either the number of LEDs

or the input voltage increases.

The graphs below can be used to select a recommended inductor to maintain the ZXLD1374 switching frequency within a

predetermined range when used in different topologies.