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RESET

STANDBY

INTERNAL

STARTUP SEQUENCE

~20 ms DELAY

BOOST STARTUP

NORMAL MODE

NRST = L

POR = H

1) TSD = L

NRST = H

and

NSTBY = H or BRC = H

EN_BOOST = H

NSTBY = L and NRST = H

EEPROM AND EEPROM

READING (~1 ms)

VREF = 95% OK

~10 ms DELAY

NSTBY = L or BRC = L

and

NRST = H

TSD = H

EN_BOOST

RISING EDGE

EN_BOOST = L

LP5520

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SNVS440B – MAY 2007 – REVISED MARCH 2016

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7.4.4 Start-Up Sequence

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 NRST input is low or internal power on reset (POR) is active. POR activates during the

chip start-up or when the supply voltage VDD falls below 1.5 V. Once VDD rises above 1.5 V, 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 power up.

STARTUP:

When <NSTBY> bit is written high or there is a rising edge in the BRC input, the INTERNAL

STARTUP SEQUENCE powers up all the needed internal blocks (Vref, Bias, Oscillator, etc.). To

ensure the correct initialization, a 10-ms delay is generated by the internal state-machine after the

trim EEPROM values are read. If the chip temperature rises too high, the thermal shutdown (TSD)

disables the chip operation, and STARTUP mode is entered until no TSD event 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 20-ms delay generated by the state machine. All LED outputs are

off during the 20-ms delay to ensure smooth start-up. The boost start-up is entered from internal

start-up 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 or the BRC input in

stand-alone mode. The registers can be written in any sequence and any number of bits can be

altered in a register in one write.

Figure 23. Device Functional Modes

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