RT4832AWSC datasheet(19/26 Pages) RICHTEK

19 / 26 page

RT4832A

is a registered trademark of Richtek Technology Corporation.

DS4832A-00

January

2017

www.richtek.com

Brightness Control

a. PWM Brightness Dimming

Besides programmable built-in I2C backlight LED

current control, the RT4832A features a built-in PWM

dimming current control by setting register 0x09[6]=1,

offering a linear current dimming by external clock

source. In order to guarantee the PWM dimming

resolution (7 bit at > 15kHz application), recommending

dimming frequency have to be operated at range of

400Hz to 20kHz.

b. I

2C Brightness Dimming

The RT4832A is built-in an I2C 10-bit or 11-bit

resolution brightness control with maximum 25mA per

string.

When LED brightness is controlled from the I2C

brightness registers (register 0x09[6]=0) , the 11-bit

brightness data is default to controls the LED current in

LED1 and LED2.

The I2C brightness dimming is the concatenation of the

two brightness registers (registers 0x04[2:0] and

0x05[7:0]). The LED current only changes when the

MSBs are written, meaning that to do a full 11-bit

current change via I2C, first the 3 MSBs are written and

then the 8 LSBs are written. It can be selected as either

linear or exponential. (register 0x02[4]).

In linear mapped mode the LED current follows the

relationship :

ILED = 0.0122mA*Brightness Code

In exponential mapped mode the LED current follows

the relationship:

ILED = 0.0183mA*(1.0035

Brightness Code )

The 11-bit exponential mapping is small enough such

that the transition from one code to the next in terms of

LED brightness is not distinguishable to the eye.

c. LED Brightness Current and PWM

The LED brightness current is controlled with the

mapping can be selected as either linear or exponential,

shows

the

Figure

The

LED

current

approximated by the equation :

With linear mapping the 10 bit code to current is

approximates by the equation :

ILED = 0.0244mA*Brightness Code*PWM Duty

With linear mapping the 11 bit code to current is

approximates by the equation :

ILED = 0.0122mA*Brightness Code*PWM Duty

With exponential mapping the 10 bit code to current is

approximates by the equation :

ILED = 0.0183mA*(1.0071

Brightness Code*PWM Duty)

With exponential mapping the 11 bit code to current is

approximates by the equation :

ILED = 0.0183mA*(1.0035

Brightness Code*PWM Duty)

10 bit LED Current vs. Linearty

Brightness Code

0.000

0.005

0.010

0.015

0.020

0.025

256

512

768

1024

Brightness Code (LSB)

10 bit LED Current vs. Exponential

Brightness Code

0.000

0.005

0.010

0.015

0.020

0.025

256

512

768

1024

Brightness Code (LSB)

RT4832AWSC Fiches technique(PDF) 19 Page - Richtek Technology Corporation

RT4832AWSC Fiches technique(HTML) 19 Page - Richtek Technology Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Fiches technique Télécharger

Lien URL