SM8132A Datasheet, PDF (13/18 Pages) Nippon Precision Circuits Inc – White LED Driver IC

SM8132A
Switching from ×1.5 mode to ×1.0 mode
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 SM8132A outputs a mode reset sig-
nal once every 1.4 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.
1.4sec/cycle
Mode reset
(1)
VOUT mode
Mode hold
L: hold
VOUT
output voltage
Low ILED
detector
1.5 mode
1.0 mode
min 80µs
max 200µs
ILED detector
ignore
(2)
(3)
4.2V ₍₄₎
(5)
Switching from ×1.5 to ×1.0 mode due to the mode reset signal
(1) Mode reset signal is output once every 1.4 seconds.
(2) Switching from ×1.5 to ×1.0 mode due to the mode reset signal pulse.
(3) The mode hold time of 200µs (max) starts when output switches to ×1.0 mode. During this interval, the
mode is not switched even if an I_LED undercurrent condition is detected.
(4) If V_IN is low, the V_OUT voltage momentarily drops because the boost function stops as a result of switching
to ×1.0 mode.
(5) The I_LED 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.
NIPPON PRECISION CIRCUITS INC.—13