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SM8133B_06 Datasheet, PDF (16/23 Pages) Nippon Precision Circuits Inc – White LED Driver IC | |||
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SM8133B
Switching from Ã1.5 mode to Ã1.0 mode
VF increases immediately after the LED current starts to ï¬ow, and then decreases as the LED temperature
increases due to the heating effect of the current ï¬ow. It can take about 10 seconds for the LED temperature to
stabilize and for VF to reach equilibrium, and VF may ï¬uctuate more than 200mV. The VF ï¬uctuation 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 SM8133B outputs a mode reset sig-
nal once every 1.4 seconds which automatically switches the output mode to Ã1.0, and then a determination is
made whether to make the Ã1.0 â Ã1.5 mode switch.
1.4sec/cycle
Mode reset
(1)
VOUT mode
(2)
1.5 mode
1.0 mode
Mode hold
L: hold
VOUT
output voltage
min 80µs
max 200µs
ILED detector
ignore
(3)
5.0V (4)
Low ILED
detector
(5)
Switching from Ã1.5 to Ã1.0 mode due to the mode reset signal
(1) Mode reset signal is output once every 1.4 seconds.
(2) Switching from Ã1.5 to Ã1.0 mode due to the mode reset signal pulse.
(3) The mode hold time of 200µs (max) starts when output switches to Ã1.0 mode. During this interval, the
mode is not switched even if an ILED undercurrent condition is detected.
(4) If VIN is low, the VOUT voltage momentarily drops because the boost function stops as a result of switching
to Ã1.0 mode.
(5) The ILED undercurrent signal is ignored during the mode hold time, and the mode only switches in
response to the detector output after the mode hold time expires.
SEIKO NPC CORPORATION â16
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