SM8135B

SEIKO NPC CORPORATION —6

(2) Setting LED current using pulse input on EN

The EN pin has a built-in counter that can be used to set the LED current to one of 14 levels (DATA1 to

first set to HIGH. The built-in counter is set to DATA1 (maximum setting), and the current is the maximum

rent change is triggered by the falling edge of the input pulse, and each pulse should have a minimum 3.0

µs

pulsewidth.

N

N: number of pulses = 0 to 13

On the 14th and 15th pulse (DATA15 and 16), the current drive circuit is shutdown and no LED drive current

flows, turning the LEDs OFF. On the 16th pulse, the current returns to the DATA1 maximum value. When the

EN input is held LOW for an interval longer than the EN hold time (1ms), the whole IC returns to standby

mode, and the LED current is set to 0. Note that the counter is also reset to value DATA1. Since the current is

still use the device to drive LEDs. In this case, the LED current setting is determined exclusively by RSET

(refer to section “(1) Setting LED drive current using RSET”).

Dimming control by EN pin

DATA

123456789

10

11

12

13

14

15

16

DIM

pulse

count

0123456789

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

[mA]

20.00

14.00

10.00

7.00

5.00

3.50

2.50

1.80

1.27

0.91

0.64

0.45

0.32

0.23

0

0

Ratio

1

1/(

(OFF)

DATA1

DATA2 DATA3 DATA4

DATA5

DATA15 DATA16

DATA1

EN hold time

EN

High

Low

turn on

1/ 2

1/ 2

1/ 2

1/ 2

turn off

(0)

turn off

(0)

turn off

(0)

turn on

1/ 2

turn off

(0)

0