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

EN = H (pin)

VLDO ok

LP8553

www.ti.com

SNVS701B – SEPTEMBER 2011 – REVISED JANUARY 2014

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) will activate

during the chip startup or when the supply voltage VLDO fall 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.

STARTUP: When BL_CTL bit is written high or PWM signal is high, the INTERNAL STARTUP 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 STARTUP: Soft start for boost output is generated in the BOOST STARTUP 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 startup. The Boost startup is entered from Internal Startup

Sequence if EN_BOOST is HIGH.

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

altered in a register in one write.

Functional Overview

LP8553 is a high-voltage LED driver for medium sized LCD backlight applications. It includes high-voltage boost

converter. Boost voltage automatically sets to the correct level needed to drive the LED strings. This is done by

monitoring LED output voltage drop in real time.

Copyright © 2011–2014, Texas Instruments Incorporated

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Product Folder Links: LP8553