SM8135A
Mode Reset Function
VF increases immediately after the LED current starts to flow, and then decreases as the LED temperature
increases due to the heating effect of the current flow. It can take about 10 seconds for the LED temperature to
stabilize and for VF to reach equilibrium, and VF may fluctuate more than 200mV. The VF fluctuation 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 fluctuation, the SM8135A outputs a mode reset sig-
nal once every 1.0 seconds which automatically switches the output mode to ×1.0, and then a determination is
made whether to make the ×1.0 → ×1.5 mode switch.
Mode reset
VOUT mode
(1)
(2)
(3)
1.0sec/cycle
1.ꢁ mode
1.0 mode
1.ꢁ mode
min ꢀ0µs
max 200µs
Mode hold
L: hold
ILED detector
ignore
4.9V
VOUT output voltage
ILED detector
(4)
Switching from ×1.5 mode to ×1.0 mode due to mode reset signal
(1) Mode reset signal is output once every 1.0 seconds.
(2) Mode switches from ×1.5 to ×1.0 mode on the rising edge of the mode reset signal.
(3) A 200µs (max) mode hold time begins after switching to ×1.0 mode. LED drive current insufficient state is
detected but the mode is not switched during this interval.
(4) LED drive current insufficient signal is ignored during the mode hold time, but normal mode switching
operation resumes when the mode hold time elapses.
SEIKO NPC CORPORATION —11
NPC [ NIPPON PRECISION CIRCUITS INC ]
