ZXLD1370

ZXLD1370

Document number: DS32165 Rev. 4 - 2

15 of 36

www.diodes.com

March 2011

© Diodes Incorporated

A Product Line of

Diodes Incorporated

Ω

=

−

=

k

110

)

1

GI

V

ADJ

V

(

1

GI

R

2

GI

R

This will result in:

Ω

=

+

=

m

150

LED

I

mV

225

)

2

GI

R

1

GI

(R

1

GI

R

s

R

Table 1

GI ratio

RGI1

RG2

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

INDUCTOR/FREQUENCY SELECTION

Recommended inductor values for the ZXLD1370 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 ZXLD1370 switching frequency within a

predetermined range when used in different topologies.

Buck inductor selection:

 

ZXLD1370 Buck Mode 1.5A Minimum Recommended Inductor

Target Switching Frequency - 400kHz

0

102030

405060

1

3

5

7

9

11

13

15

Supply Voltage (V)

L=10µH

L=22µH

L=33µH

L=47µH

Figure 19. 1.5A Buck mode inductor selection for target frequency of 400 kHz