LP39542 Datasheet, PDF (7/58 Pages) National Semiconductor (TI) – Advanced Lighting Management Unit

Modes of Operation
RESET:
In the RESET mode all the internal registers are reset to the default values and the chip goes to STANDBY
mode after reset. NSTBY control bit is low after reset by default. Reset is active always if NRST input pin is
low or internal Power On Reset is active. LP39542 can be also reset by writing any data to Reset Register
in address 60H. Power On Reset (POR) will activate during the chip startup or when the supply voltage
V_DD2 falls below 1.5V. Once V_DD2 rises above 1.5V, POR will inactivate and the chip will continue to the
STANDBY mode.
STANDBY:
The STANDBY mode is entered if the register bit NSTBY is LOW. 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 power up.
STARTUP:
When NSTBY bit is written high, the INTERNAL STARTUP SEQUENCE powers up all the needed internal
blocks (Vref, Bias, Oscillator etc..). To ensure the correct oscillator initialization, a 10 ms delay is generated
by the internal state-machine. If the chip temperature rises too high, the Thermal Shutdown (TSD) 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 PFM
mode during the 10 ms delay generated by the state-machine. The Boost startup is entered from Internal
Startup Sequence if EN_BOOST is HIGH or from Normal mode when EN_BOOST is written HIGH. During
the 10 ms Boost Startup time all LED outputs are switched off to ensure smooth start-up.
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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