SM8133B_06 Datasheet, PDF (15/23 Pages) Nippon Precision Circuits Inc – White LED Driver IC

SM8133B
Switching from ×1.0 mode to ×1.5 mode
If the LED drive current set by serial interface can be driven 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 5.0V. 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 LED drive current set by serial interface 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 automati-
cally 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 7-channel LED drive circuits, thus it is recommended that LEDs
have small “VF” variation to optimize the total efficiency.
VIN
input voltage
Low ILED
detector
VOUT mode
1.0 mode
VOUT
output voltage
Low ILED
detected
1.5 mode
1.0 1.5 threshold
(1)
(2)
5.0V ₍₃₎
V_IN voltage drop and V_OUT output voltage
(1) When V_IN falls, V_OUT cannot overcome the LED “VF” rating, causing insufficient current flows and the
I_LED low-current signal becomes active.
(2) When the I_LED low-current condition is detected, the V_OUT output circuit switches to ×1.5 mode (charge
pump mode).
(3) Prior to switching to ×1.5 mode, the V_OUT voltage may be lower than 5.0V but sufficient current is sup-
plied to the LED.
If after startup, the LED connected to a DIN pin is switched, the LED connection detector circuit flags an error,
and correct mode switching may not occur. If the DIN pin does not control the LED drive current, the low-cur-
rent detector does not operate and the device cannot switch to ×1.5 mode.
SEIKO NPC CORPORATION —15