LP55281TLSLASHNOPB datasheet(23/42 Pages) TI2

23 / 42 page

LP55281

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SNVS458D – JUNE 2007 – REVISED OCTOBER 2016

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7.4 Device Functional Modes

7.4.1 Modes Of Operation

RESET:

In the RESET mode all the internal registers are reset to the default values and the device goes to

STANDBY mode after reset. NSTBY control bit is low after reset by default. Reset is entered

always if Reset Register is written, internal Power On Reset is active, or NRST pin is pulled down

externally. The LP55281 can be reset by writing any data to the Reset Register (address 60H).

Power On Reset (POR) will activate during the device startup or when the supply voltage VDD2 falls

below 1.5 V. Once VDD2 rises above 1.5V, POR inactivates, and the device continues 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 startup.

STARTUP:

When NSTBY bit is written high, the INTERNAL STARTUP SEQUENCE powers up all the needed

internal blocks (VREF, Oscillator, etc.). To ensure the correct oscillator initialization, a 10 ms delay

is generated by the internal state-machine. If the device temperature rises too high, the Thermal

Shutdown (TSD) disables the device operation and STARTUP mode is entered until no thermal

shutdown is present.

BOOST STARTUP: Soft start for boost output is generated in the BOOST STARTUP mode. The boost output is

raised in PWM 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 startup.

NORMAL:

During NORMAL mode the user controls the device 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.

LP55281TL/NOPB Datasheet(PDF) 23 Page - Texas Instruments