AN4291 datasheet(41/53 Pages) STMICROELECTRONICS

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AN4291

Measurements

Figure 22. Current regulation vs. VPW_LED: 10 LEDs

8.4

Current regulation validation

The Table 5 compares the real current values, as captured by the oscilloscope, with the

expected ones as configured by the user. The input power voltage is fixed and set at the

middle of the usable range. The current is the mathematical average current (not the peak

current) as got and calculated by the scope.

8.5

OCP protection time

Figure 23, Figure 24 and Figure 25 show the current protection reaction time. The current

working point is fixed at 245 mA in the first plot, at 738 mA in the second and at the

0.2

0.4

0.6

0.8

1.2

13V

16V

20V

24V

28V

32V

36V

40V

44V

48V

1.065A

738mA

492mA

329mA

254mA

AM16722v1

Table 5. Current regulation discrepancies

Command

3 LEDs – 20 V

6 LEDs – 32 V

10 LEDs – 44 V

Expected

lc x 0

0.251 A

0.254 A

0.255 A

0.245 A

lc x 1

0.329 A

0.333 A

0.329 A

lc x 2

0.407 A

0.414 A

0.413 A

0.410 A

lc x 3

0.486 A

0.493 A

0.492 A

lc x 4

0.563 A

0.571 A

0.570 A

0.574 A

lc x 5

0.639 A

0.647 A

0.646 A

0.648 A

lc x 6

0.715 A

0.725 A

0.724 A

0.738 A

lc x 7

0.791 A

0.802 A

0.800 A

0.819 A

lc x 8

0.867 A

0.879 A

0.877 A

0.901 A

lc x 9

0.943 A

0.957 A

0.955 A

0.984 A

lc x 10

1.016 A

1.031 A

1.030 A

1.065 A

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