SM8132A Datasheet, PDF (8/18 Pages) Nippon Precision Circuits Inc – White LED Driver IC

SM8132A
FUNCTIONAL DESCRIPTION
LED Drive Current Setting
The SM8132A LED drive current setting is controlled by the combination of resistance connected to ISET and
the EN input signals.
(1) Setting LED Drive Current using RSET
The maximum drive current per LED (when DATA = 1) is determined by the external resistance connected to
ISET. For example, if I_{LED MAX} = 15mA, from the graph below, a resistance “RSET” of 15kΩ should be con-
nected between ISET and GND. Note that while RSET can have a maximum resistance 50kΩ, the total LED
output current must not exceed the maximum output current of 80mA.
ISET
RSET
GND
50
40
30
20
10
0
0
10
20
30
40
50
RSET [kΩ]
LED drive current maximum setting using RSET
(2) Setting LED Drive Current using EN Input Signals
The EN input ENABLE/DISABLE circuit, also simultaneously counts the number of input pulses using an
internal counter and adjusts the LED drive current setting in response. The internal 4-bit counter provides 16-
step (DATA = 1 to 16) adjustment, where each step is 1/15th of the maximum current (I_{LED MAX}) set by RSET.
On the 16th pulse (DATA = 16), the LED drive current control circuit shuts down. On the 17th pulse (DATA =
1), the LED drive current is reset to the maximum current value. As the current is set to the maximum value on
the first pulse, applications without pulse input can also be employed (by controlling brightness using RSET).
EN
123
EN input
pulse
GND
25
20
15
10
5
0
0
RSET=10kΩ
RSET=15kΩ
RSET=20kΩ
4
8
12
16
DATA set by EN input pulse
LED drive current setting variation using EN input
pulse modulation
Table. LED drive current setting and EN input pulse count
DATA 1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
EN
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
pulse
count 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
49 50 51
I_LED 15/15 14/15 13/15 12/15 11/15 10/15 9/15 8/15 7/15 6/15 5/15 4/15 3/15 2/15 1/15 0
NIPPON PRECISION CIRCUITS INC.—8