SM8132A Datasheet, PDF (11/18 Pages) Nippon Precision Circuits Inc – White LED Driver IC

SM8132A
Switching to power-save mode
The internal circuit operating mode switches from ×1.0/×1.5 mode to power-save mode when EN goes LOW
and do not switch HIGH for an interval of 1.63ms (max). This function turns the LEDs OFF and automatically
transfers internal circuit control to power-save mode, suppressing current consumption.
EN
Internal
enable (CE)
Power
save
1.0 or 1.5
CE hold time 1.63ms (max)
Power
save
EN input signal and internal enable signal “CE”
I If the EN input signal is held for an interval greater than the “CE” hold time 1.63ms (max), the SM8132A
switches to power-save mode. The internal circuits are reset on the “CE” falling edge, and the current setting
must be re-established before restart.
Switching from ×1.0 mode to ×1.5 mode
If the LEDs can be driven solely by the current determined by RSET and EN pulse input without boosting the
V_IN input voltage, the V_OUT output operates in ×1.0 mode. In other words, if sufficient current flows even with
the LED forward-direction voltage drop “VF”, then V_OUT is less than 4.2V. Operation in the more efficient
×1.0 mode reduces the total power dissipation and extends the battery drive time. And if low “VF” LEDs are
used or the LED drive current setting is LOW, the operating time in ×1.0 mode is also extended.
1.0 mode
(high efficiency)
High VF LED
1.5 mode
(low efficiency)
1.0 mode
(high efficiency)
Low VF LED
High
VIN input
1.5 mode
(low efficiency)
Low
V_OUT mode switching time comparison due to drive LED “VF” variation
If the V_IN voltage falls or RSET increases such that the LED drive current is too low in ×1.0 mode, then the
LED drive circuit low-current detector operates, the V_OUT output is automatically switched to ×1.5 mode, and
the charge pump boosts the output voltage. This occurs even if only one LED low-current condition is detected
among the 4-channel LED drive circuits, thus it is recommended that LEDs have small “VF” variation to opti-
mize the total efficiency.
NIPPON PRECISION CIRCUITS INC.—11