SM8136A Datasheet, PDF (5/15 Pages) Nippon Precision Circuits Inc – White LED Driver IC

SM8136A
FUNCTIONAL DESCRIPTION
LED Drive Current Setting
The SM8136A LED drive current can be set using the EN pin. The EN input is used to enable/disable circuit
operation. It also is used by a built-in counter that counts the number of input pulses in order to set the LED
current value. The built-in counter is a 4-bit counter for 16-step adjustment (DATA = 1 to 16). On the 16th
pulse (DATA = 16), the LED current drive circuit shuts down and LED current is zero. On the 17th pulse
(DATA = 1), the current returns to the maximum value. As the initial pulse (DATA = 1) sets the current to the
maximum value, the device can also be used in applications that do not support pulsed input.
Table 1. EN input pulse count and LED current setting values
DATA 1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
EN
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
pulse
count 17 18 19 20 21 22 23 24
I_LED
[mA]
20.00 18.7
17.3
16.0
14.7
13.3
12.0
10.7
9.3
8.0
6.7
5.3
4.0
2.7
1.3
0
EN Input Signal and LED Current Setting (Initialization)
On the first rising edge of EN, the internal startup signal goes HIGH and LED current will start to flow after the
soft start time has elapsed. As the LED current setting is adjusted by counting the number of input pulses on
EN, the EN input voltage must be switched HIGH → LOW → HIGH repeatedly to set the current to a lower
value. After the desired value is achieved, the EN input voltage is held HIGH to maintain the LED current set-
ting. If the EN input goes LOW, the LED current does not flow. The EN data input circuit operates even though
the LED current does not flow during the soft start interval, but as long as the current value is set during the soft
start interval the LED drive circuits will start to drive the LEDs with that constant current setting. However,
note that the setting is valid only after the power-ON reset when the VIN supply is applied. Accordingly, allow
1ms or more after connecting the VIN supply before setting the current value using the EN input.
EN input
signal
ILED1-3
12345
678
1
2
3
4
5
6
7
8
EN input signal and LED current setting
I LED current setting is determined by the number of EN input signal rising edges. Furthermore, no LED cur-
rent flows until the soft start time has elapsed.
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