LP8550TLESLASHNOPB.A datasheet(21/49 Pages) TI2

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STANDBY

RESET

INTERNAL

STARTUP

SEQUENCE

EN = L (VLDO low)

or POR = H

EN_BOOST = 1*

TSD = H

~2 ms Delay

BOOST STARTUP

EN = H (pin) and BL_CTL = 1

or PWM = H (pin)

BL_CTL = 0 and

PWM = L

EN_BOOST = 0*

~4 ms Delay

NORMAL MODE

EN_BOOST

rising edge*

*) TSD = L

VREF = 95% OK*

EN = H (pin)

VLDO ok

LP8550

www.ti.com

SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014

8.4 Device Functional Modes

Figure 19. Modes of Operation

RESET:

In the RESET mode all the internal registers are reset to the default values. Reset is entered

always when VLDO voltage is low. EN pin is enable for the internal LDO. Power On Reset (POR)

activates during the chip startup or when the supply voltage VLDO falls below POR level. Once

VLDO rises above POR level, POR will inactivate, and the chip will continue to the STANDBY

mode.

STANDBY: The STANDBY mode is entered if the register bit BL_CTL is LOW and external PWM input is not

active and POR is not active. This is the low power consumption mode, when only internal 5V LDO

is enabled. Registers can be written in this mode, and the control bits are effective immediately

after start-up.

START-UP: When BL_CTL bit is written high or PWM signal is high, the INTERNAL START-UP SEQUENCE

powers up all the needed internal blocks (VREF, Bias, Oscillator etc.). Internal EPROM and

EEPROM are read in this mode. To ensure the correct oscillator initialization, etc., a 2-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 START-UP: Soft start for boost output is generated in the BOOST START-UP mode. The boost output

is raised in low current PWM mode during the 4 ms delay generated by the state-machine. All LED

outputs are off during the 4-ms delay to ensure smooth start-up. The Boost start-up is entered from

Internal Start-up Sequence if EN_BOOST is HIGH.

NORMAL:

During NORMAL mode the user controls the chip using the external PWM input or with Control

Registers through I2C. 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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