LP3954RLSLASHNOPB datasheet(8/60 Pages) TI1

8 / 60 page

STANDBY

RESET

INTERNAL

STARTUP

SEQUENCE

Reset Register write

or POR = H

EN_BOOST = H*

THSD = H

~10 ms Delay

BOOST STARTUP

NSTBY = H

NSTBY = L

EN_BOOST = L*

~10 ms Delay

NORMAL MODE

EN_BOOST

rising edge*

* THSD = L

VREF = 95% OK*

POR = L

LP3954

SNVS340D – JUNE 2005 – REVISED MARCH 2013

www.ti.com

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 entered always if

Reset Register is written or internal Power On Reset is active. There is no dedicated Reset pin available.

LP3954 can be 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 VDD2 falls below 1.5V. Once VDD2 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 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 PFM mode during the 10ms 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 10ms 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

Figure 1. Modes of Operation

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