SM8132A Datasheet, PDF (9/18 Pages) Nippon Precision Circuits Inc – White LED Driver IC

SM8132A
EN input signal and LED drive current setting (startup)
An internal startup signal goes HIGH on the first rising edge of EN, and LED drive current starts after the soft-
start time expires. The LED drive current control circuit sets the current by counting the input pulses on EN,
hence the EN input voltage must be switched HIGH → LOW → HIGH the required number of data steps to
reduce the current setting. When the desired setting is reached, the EN input voltage should be tied HIGH to
maintain the setting. Note that the LED drive current does not flow when EN is LOW.
The EN data input circuit operates during the soft-start time when no LED drive current flows, hence the cur-
rent setting can be adjusted during the soft-start time and the LED drive circuit will then start at the desired cur-
rent setting. However, setting the current using EN signal pulses is possible only when the power-ON reset
ends after a rising edge on the VIN supply. Consequently, a delay of 1ms or greater should be allowed after
VIN is applied before starting the EN input signals.
EN
input signal
ILED 1 to 4
12345
678
1234
5
678
EN input signal and LED drive current setting
I The LED drive current is set by the number of EN input signal rising-edge. The LED drive current control
circuit is disabled, and the LED drive current does not flow during EN input signal LOW interval or at star-
tup until after the soft-start time expires.
EN input signal and LED drive current setting (disable interval)
The LED drive current setting due to EN input is set by the 4-bit counter (16 steps). On the 17th pulse, the
counter DATA = 1 and the current is reset to the maximum current value. When the counter DATA = 16, I_LED =
0mA and the LED drive circuit shuts down.
EN input
11 12 13 14 15 16 17 18 19 20 21
ILED
disable signal
ILED
off
ILED 1 to 4
12345
11 12 _{13 14 15 16}
LED drive current setting disable interval
When EN is held LOW for an extended interval, the internal enable signal “CE” goes LOW and the device
enters power-save mode. In this mode, the EN input internal counter is reset and subsequent rising-edge pulses
on EN restart the counter from DATA = 1.
NIPPON PRECISION CIRCUITS INC.—9