SM8133B_06 Datasheet, PDF (14/23 Pages) Nippon Precision Circuits Inc – White LED Driver IC

SM8133B
LDO (Low Dropout Voltage Regulator)
Operation is controlled using the LDO register (LSB in address “5H”). When the LDO register is set to 1, a
regulated stable voltage is output from LDOUT. If the overcurrent protection circuit connected to LDOUT
detects a continuous overcurrent condition for approximately 200µs, the LDO output stops and then restarts
after a delay of approximately 1.4 seconds. At this point, if an overcurrent condition is detected again, the LDO
output stops. If the overcurrent condition is detected a total of 12 successive times (approximately 16.8 sec-
onds), the LDO load is deemed to be abnormal and the LDO output stops completely. The abnormal load con-
dition is released only by selecting reset mode operation.
Thermal Shutdown Circuit (Overheating Protection)
The thermal shutdown circuit operates whenever the IC temperature exceeds approximately 180°C for what-
ever reason. VOUT output recommences when the IC temperature falls below approximately 160°C.
RESETB Input (Internal Circuit Reset Signal)
If the microcontroller, which drives the serial data inputs, stops, the SM8133B logic-level signal inputs are left
floating and the SM8133B will most likely not transfer to standby mode normally. However, the RESETB pin
can be connected to the microcontroller supply pin, so that the SM8133B is reset automatically whenever the
voltage on RESETB drops. A pull-down resistor should be connected between RESETB and GND to avoid a
floating RESETB input with voltage applied to the VIN pin.
V_OUT Output Circuit Mode Switching
The SM8133B switches between 3 output states: power-save mode (standby state), ×1.0 mode (VIN through
mode), and ×1.5 mode (×1.5 charge pump boost). This automatically adjusts the VOUT output to match the
drive LED characteristics and reduces the total power dissipation. Switching to and from ×1.0 and ×1.5 mode
occurs automatically in an internal circuit, and cannot be controlled using an external input.
Switching to standby mode
The internal circuit operating mode switches from ×1.0/×1.5 mode to standby mode when Reset resistor (mode
data “0H”, “EH”) was input, suppressing current consumption.
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