LP85571 datasheet(30/49 Pages) TI2

30 / 49 page

LP8557, LP85571

SNVSA15B – DECEMBER 2013 – REVISED DECEMBER 2015

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8.6.1.9 LEDEN

Address: 0x14h

Reset: 0xBFh (LP8557I)

ENABLE[6:1]

Bits

Field

Type

Default

Description

7:6

reserved

R/W

10b

5:0

ENABLE

R/W

111111b

LED string enables.

000001 = Only 1 current sink enabled.

001111 = Current sinks 1-4 enabled.

011111 = Current sinks 1-5 enabled.

111111 = All 6 current sinks enabled (Default)

The ENABLE field configures the strings if the AUTO bit is 0. The LP8557I allows re-configuration of the

ENABLE bits via I2C writes. Note that re-configuration must be done every time the power on the VDD pin is

recycled.

8.6.1.10 STEP

Address: 0x15h

Reset: 0x00h (LP8557I)

SMOOTH[1:0]

—

STEP[1:0]

Bits

Field

Type

Default

Description

7:6

SMOOTH

R/W

00b

Filter strength for digital smoothing filter.

00 = no smoothing (Default)

10 = light smoothing

10 = medium smoothing

11 = heaving smoothing

5:2

reserved

R/W

0000b

1:0

STEP

R/W

00b

Ramp time for a 0% to 100% current change.

00 = 0 ms (Default)

01 = 50 ms (12.2 µs/12-bit LSB)

10 = 100 ms (24.4 µs/12-bit LSB)

11 = 200 ms (48.8 µs/12-bit LSB)

On LP8557I, it is possible to enable slope and advanced slope functions by re-configuration of the STEP and

SMOOTH bits appropriately via I2C writes. Note that re-configuration must be done every time power on the VDD

pin is recycled.

The STEP field controls the rate of brightness level changes (slope function). Brightness transitions have a fixed

step time. The time required to complete a ramp between two levels also depends upon the difference between

the starting and ending current levels. For example, when STEP is set to 10b a brightness transition from 0% to

100% takes 100 ms, while a transition from 50% to 100% takes 50 ms.

The SMOOTH field controls the digital smoothing filter (advanced slope function). This filter behaves much like

an RC filter. It can be used to remove the overshoot that appears to occur on large brightness changes. The

actual amount of smoothing is tailored for the STEP field setting. For example, medium filter strength is higher for

100-ms ramp times than for 50-ms ramp times. This gives 16 possible brightness-level ramping configurations.

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