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5

RD-0608

Since some of these equivalent values of resistance are not available, series and parallel combinations are used and

are specified as follows (all combinations use standard value resistors: 1.43Ω, 0.56Ω, and 0.47Ω):

Ω

= 43

.

1

350mA

R

Ω

=

Ω

Ω

≈

Ω

=

715

.

0

)

43

.

1

||

43

.

1

(

71

.

0

700mA

R

Ω

=

Ω

+

Ω

Ω

+

Ω

≈

Ω

=

515

.

0

)

56

.

0

47

.

0

(

||

)

56

.

0

47

.

0

(

5

.

0

1A

R

Ω

=

Ω

+

Ω

Ω

+

Ω

Ω

+

Ω

≈

Ω

=

343

.

0

)

56

.

0

47

.

0

(

||

)

56

.

0

47

.

0

(

||

)

56

.

0

47

.

0

(

33

.

0

5

.

1 A

R

Although some of the series and parallel combinations do not yield the exact resistance needed for tolerance

purposes, they are accurate enough. For this evaluation board an extremely tight current regulation is achieved with

a worst case result of ±1.2% for the 350mA setting over the bus voltage range from 50V to 170V. Likewise a precise

regulation of ±0.25% can be maintained for a range of load voltage from 16V to 24V at the 350mA current setting.

The jumper positions on the evaluation boards (JSET) for setting the different load currents are shown below:

Fig. 4a: JSET LED Current Programming Settings

Fig. 5 Vout = 16V, L1 = 470uH, COUT = 33uF

0

200

400

600

800

1000

1200

1400

1600

30

50

70

90

110

130

150

170

Vin (V)

350mA

700mA

1A

1.5A

±1.2%

±0.6%

±0.5%

±0.3%