LP8555 datasheet(48/64 Pages) TI1

48 / 64 page

LP8555

SNVS857 – FEBRUARY 2014

www.ti.com

Typical Applications (continued)

ADDRESS

BIT

BIT NAME

BIT DESCRIPTION

VALUE

MEANING

REG VALUE

(HEX)

7:6

FMOD_DIV

Spread spectrum modulation frequency

00b

When COMMAND.SSEN is set to 1

divisor

this value is used.

00 = 0.42%

5:0

010111b

6:4

VHR_SLOPE

LED driver maximum headroom voltage at

110b

110 = 285 mV

maximum current (50mA)

2:0

VHR_VERT

LED driver maximum headroom voltage at

000b

000 = 50 mV

minimum current

5:4

VHR_HYST

LED driver hysteresis for mid comparator

01b

01 = 233 mV

level

3:2

00b

1:0

VHR_HORZ

LED driver headroom control knee

01b

01 = 25%

percentage of full LED current

JEN

Enable boost voltage jumping on

1 = Jump enabled

brightness change

6:4

000b

3:2

JTHR

Jump brightness threshold

10b

10 = 25%

1:0

JVOLT

Jump voltage

00b

00 = 2 V

9.2.1.3 Design Requirements

Example requirements based on default EPROM setup.

DESIGN PARAMETER

EXAMPLE VALUE

Input voltage range

2.7 V to 4.5 V (Single Li-Ion cell battery)

Brightness Control

PWM input duty cycle

Backlight enabled

Writing ON bit 1 with I2C

PWM output frequency

19.2 kHz with PSPWM enabled

LED Current

25 mA / channel

Number of Channels

Up to 12 with string auto detection enabled

Brightness slopes

Disabled

External set resistors

Disabled

Inductor

4.7 µH to 6.8 µH, at least 3.1-A saturation current

Boost SW frequency

1 MHz

Maximum output voltage

28 V

SW current limit

3.1 A

CABC

Jump enabled for >25% brightness changes

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