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SM8136A Datasheet, PDF (9/15 Pages) Nippon Precision Circuits Inc – White LED Driver IC | |||
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SM8136A
Switching from Ã1.5 Mode to Ã1.0 Mode
The LED VF increases immediately after the LED current starts to ï¬ow, and then decreases as the LED temper-
ature increases due to the heating effect of the current ï¬ow. It can take about 10 seconds or more for the LED
temperature to stabilize and for VF to reach equilibrium, and VF may ï¬uctuate more than 200mV. The VF ï¬uc-
tuation is affected by the ambient temperature and LED current setting, and has a large affect on the automatic
mode switching voltage tolerances. To counter the effects of VF ï¬uctuation, the SM8136A outputs a mode
reset signal once every 1.0 seconds which automatically switches the output mode to Ã1.0, and then a determi-
nation is made whether to make the Ã1.0 â Ã1.5 mode switch.
Mode reset
1.0sec/cycle
(1)
VOUT mode
Mode hold
L: hold
VOUT voltage
1.5 mode
1.0 mode
min 80µs
max 200µs
ILED detector
ignore
1.5 mode
(2)
(3)
5.0V
ILED detector
(4)
Switching from Ã1.5 mode to Ã1.0 mode due to mode reset signal
(1) Mode reset signal is output once every 1.0 seconds.
(2) Mode switches from Ã1.5 to Ã1.0 mode on the rising edge of the mode reset signal.
(3) A 200µs (max) mode hold time begins after switching to Ã1.0 mode. LED drive current insufï¬cient state is
detected but the mode is not switched during this interval.
(4) LED drive current insufï¬cient signal is ignored during the mode hold time, but normal mode switching
operation resumes when the mode hold time elapses.
SEIKO NPC CORPORATION â9
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