SM8136A Datasheet, PDF (6/15 Pages) Nippon Precision Circuits Inc – White LED Driver IC

SM8136A
V_OUT Output Circuit Mode Switching
The SM8136A output mode switches between 3 operating modes in response to the operating conditions. The
modes are: standby mode, ×1.0 mode (VIN through mode), and ×1.5 mode (1.5-times charge pump boost). The
VOUT output switches automatically between these modes in response to the drive LED characteristics and the
overall power consumption. Switching from ×1.0 mode to ×1.5 mode is controlled automatically by an internal
circuit. The operating mode cannot be specified by an external control signal.
Startup: Internal Reset Time and Soft Start Time
The SM8136A normal startup procedure (after VIN has been applied previously) is to switch from standby
mode to the ×1.0/×1.5 operating modes when the EN enable input goes HIGH. The soft start time (described
on the following page) begins after switching to the operating mode using EN.
VIN High
VIN
EN Standby mode
(1)
Soft start time
ENABLE ON
(2)
Normal startup
(1) VIN is HIGH, EN is LOW (standby mode)
(2) Switches to an operating mode when EN goes HIGH (soft start time begins)
If the use at EN = VIN when power is applied, the startup commences after the power-ON reset (POR) time
(approximately 50µs) has elapsed.
< 50µs
EN = VIN
2.7V
(1)
0.3V
Internal
power on
POR time
(2)
reset
typ: 50µs
Internal
Soft start time
enable
(3)
(CE)
Standby mode
1.5 mode
Internal reset operation when power is applied (power-ON reset)
(1) When using at EN = VIN, rising time from 0.3V to 2.7V should set < 50µs.
(2) Power-ON reset (POR) circuit resets internal circuits approximately 50µs after the power is applied.
(3) If EN is HIGH when power is applied, the internal circuits start operating when the internal “CE” signal ris-
ing edge occurs after the power-ON reset time. If EN is LOW when power is applied, the “CE” rising edge
occurs simultaneously with the first rising edge.
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