LP3958 Datasheet, PDF (7/28 Pages) National Semiconductor (TI) – Lighting Management Unit with High Voltage Boost Converter

Modes of Operation
RESET:
In the RESET mode all the internal registers are reset to the default values. Reset is entered always if input
NRST is LOW or internal Power On Reset is active. Power On Reset (POR) will activate during the chip
startup or when the supply voltages V_DD1 and V_DD2 fall below 1.5V. Once V_DD1 and V_DD2 rises above 1.5V,
POR will inactivate and the chip will continue to the STANDBY mode. NSTBY control bit is low after POR
by default.
STANDBY:
The STANDBY mode is entered if the register bit NSTBY is LOW and Reset is not active. This is the low
power consumption mode, when all circuit functions are disabled. Registers can be written in this mode and
the control bits are effective immediately after start up.
STARTUP:
When NSTBY bit is written high, the INTERNAL STARTUP SEQUENCE powers up all the needed internal
blocks (V_REF, Bias, Oscillator etc.). To ensure the correct oscillator initialization, a 10ms delay is generated
by the internal state-machine. If the chip temperature rises too high, the Thermal Shutdown (THSD)
disables the chip operation and STARTUP mode is entered until no thermal shutdown event is present.
BOOST STARTUP: Soft start for boost output is generated in the BOOST STARTUP mode. The boost output is raised in low
current PWM mode during the 20ms delay generated by the state-machine. All LED outputs are off during
the 20ms delay to ensure smooth startup. The Boost startup is entered from Internal Startup Sequence if
EN_BOOST is HIGH or from Normal mode when EN_BOOST is written HIGH.
NORMAL:
During NORMAL mode the user controls the chip using the Control Registers. The registers can be written
in any sequence and any number of bits can be altered in a register in one write.
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