LP8555 datasheet(34/64 Pages) TI1

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LP8555

SNVS857 – FEBRUARY 2014

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8.5.5 CONFIG

Address: 0x10

PWMSB

PWMFILT

EN_BPHASE180

RESERVED

RELOAD

AUTO

BRTMODE

Bits

Field

Type

Description

Enables PWM standby mode

PWMSB

R/W

0 = CONTROL.ON alone turns the backlight on/off

1 = turn off the backlight after 50 ms of PWM low

0 = PWM input filter disabled

PWMFILT

R/W

1 = Enable 50 ns glitch filter on PWM input.

0 = Boosts operate in same phase

EN_BPHASE180

R/W

1 = Enable 180° phase shift between the 2 boost switchers.

reserved

R/O

Automatically re-read the EPROM at each turn-on.

RELOAD

R/W

0 = only read the EPROM upon power-up

1 = re-read the EPROM when the backlight turns on

Automatic LED string configuration

AUTO

R/W

0 = enable LED strings using just LEDEN.ENABLE

1 = disable all open LED strings

Brightness mode

00 = PWM

1:0

BRTMODE

R/W

01 = BRTHI/BRTLO registers

10 = PWM × unshaped BRTHI/BRTLO registers

11 = BRTHI/BRTLO registers × unshaped PWM

When the AUTO bit is set the LED configuration is done dynamically. When an OPEN/SHORT condition is

detected on an LED string it will be removed, and PWM output phasing will be adjusted. Conversely, an LED

string will be added back for operation if the LED string is not open.

The BRTMODE field selects how LED brightness is controlled. When BRTMODE is set to 00b the PWM/INT

terminal duty cycle controls the LED brightness. When BRTMODE is set to 01b the BRTLO and BRTHI registers

will control the LED brightness. When the backlight is turned on the brightness level is reset to 0% and will

automatically transition to the brightness value programmed in the BRTLO and BRTHI registers.

When the BRTMODE field is set to 00b, and the PWMSB bit is set to 1, the backlight will be turned off whenever

the PWM/INT terminal is held low for 50 ms. This will also put the device into its lowest power state. When the

PWM/INT terminal becomes active the backlight will automatically turn back on.

A 50 ns glitch filter will be applied to the PWM input signal when the PWMFILT bit is set to 1. When BRTMODE

is set to 10b or 11b the LED brightness is controlled by both the PWM/INT terminal duty cycle and the BRTLO

and BRTHI registers.

When BRTMODE is set to 10b the PWM/INT terminal duty cycle is routed through the smoothing function

(controlled via the STEP register). The smoothed duty cycle is multiplied with the value from the BRTLO/BRTHI

registers. Updates to the BRTLO/BRTHI registers have an immediate effect on the LED brightness, while

PWM/INT terminal duty cycle changes may be smoothed.

When BRTMODE is set to 11b the BRTLO/BRTHI register value is routed through the smoothing function. The

smoothed brightness level is multiplied with the PWM/INT terminal duty cycle. In this configuration PWM/INT

terminal duty cycle changes have an immediate effect on the LED brightness, while BRTLO/BRTHI register

changes may be smoothed.

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