SM8135A
Boost Mode Auto-switching
The SM8135A switches between ×1.0 mode (VIN through mode), ×1.5 mode (1.5-times charge pump boost),
and ×2.0 mode (2.0-times charge pump boost) automatically in response to the operating state to reduce current
consumption. The switching transition flow chart is shown in the following figure.
LED ON
1.0 mode
1.ꢁ mode
insufficient
ILED judgment
ILED judgment
sufficient
insufficient
sufficient
1.ꢁ mode
2.0 mode
1.0sec
1.0sec
Mode reset
Mode reset
2.0 1.ꢁ
1.ꢁ
1.0
ILED judgment
ILED judgment
sufficient
sufficient
insufficient
insufficient
Boost mode switching flow chart
This section describes the boost mode switching in response to insufficient LED drive current level detection.
The next section describes the mode reset functions. Initially, when the LED drive current begins to flow, oper-
ation begins in ×1.0 mode at the set current value if possible, without boosting the input voltage VIN. If the set
current value cannot be attained in ×1.0 mode due to a VIN voltage drop or an increase in the set current value,
a low-current detector circuit connected to each LED drive circuit is activated that switches the VOUT output
to ×1.5 mode automatically, and the charge pump circuit starts boosting the voltage by 1.5 times. If the set cur-
rent value still cannot be attained, the LED drive circuits are switched to ×2.0 mode, and the charge pump starts
boosting the voltage by 2 times.
SEIKO NPC CORPORATION —9
NPC [ NIPPON PRECISION CIRCUITS INC ]
