19

FN6434.2

December 22, 2008

PWM Brightness Control Register (0x00)

The Brightness control resolution has 256 steps of PWM duty

cycle adjustment. The bit assignment is shown in Figure 23. All

of the bits in this Brightness Control Register can be read or

write. Step 0 corresponds to the minimum step where the

current is less than 10µA. Steps 1 to 255 represent the linear

steps between 0.39% and 100% duty cycle with approximately

0.39% duty cycle adjustment per step.

• An SMBus Write Byte cycle to Register 0x00 sets the

PWM brightness level only if the backlight controller is in

SMBus mode (see Table 3 Operating Modes selected by

Device Control Register Bits 1 and 2).

• An SMBus Read Byte cycle to Register 0x00 returns the

programmed PWM brightness level, regardless of the

value of PWM_SEL.

• An SMBus setting of 0xFF for Register 0x00 sets the

backlight controller to the maximum brightness.

• An SMBus setting of 0x00 for Register 0x00 sets the

backlight controller to the minimum brightness output in

which the LED current is guaranteed to be less than 10µA.

• Default value for Register 0x00 is 0xFF.

Device Control Register (0x01)

This register has 2 bits that control the operating mode of the

backlight controller and a single bit that controls the BL

ON/OFF state. The remaining bits are reserved. The bit

assignment is shown in Figure 24. All other bits in the Device

Control Register will read as low unless otherwise written.

Bits 7 and 6 are not implemented and will always read low.

TABLE 2B. DATA BIT DESCRIPTIONS

ADDRESS

REGISTER

DATA BIT DESCRIPTIONS

0x00

PWM Brightness Control Register BRT[7..0] = 256 steps of DPWM duty cycle brightness control

0x01

Device Control Register

PWM_MD = PWM mode select bit (1 = absolute brightness, 0 = % change), default = 0

PWM_SEL = Brightness control select bit (1 = control by PWMI, 0 = control by SMBus), default = 0

BL_CTL = BL On/Off (1 = On, 0 = Off), default = 0

0x02

Fault/Status Register

2_CH_SD = Two LED output channels are shutdown (1 = shutdown, 0 = OK)

1_CH_SD = One LED output channel is shutdown (1 = shutdown, 0 = OK)

BL_STAT = BL status (1 = BL On, 0 = BL Off)

OV_CURR = Input overcurrent (1 = Overcurrent condition, 0 = Current OK)

THRM_SHDN = Thermal Shutdown (1 = Thermal fault, 0 = Thermal OK)

FAULT = Fault occurred (Logic “OR” of all of the fault conditions)

0x03

Identification Register

MFG[3..0] = Manufacturer ID (16 vendors available. Intersil is vendor ID 9)

REV[2..0] = Silicon rev (Rev 0 through Rev 7 allowed for silicon spins)

0x07

DC Brightness Control Register

BRTDC[7..0] = 256 steps of DC brightness control

0x08

Configuration Register

VSC[1..0] = Short circuit thresholds selection

FSW[2] = Switching frequencies selection

0x09

Output Channel Mask/Fault

Readout Register

CH[5..0] = Output Channel Read and Write. In Write, 1 = Channel Enabled, 0 = Channel Disabled.

In Read, 1 = Channel OK, 0 = Channel Not OK/Channel disabled

PWM_MD PWM_SEL

MODE

X

1

PWMI Mode

1

0

SMBus Mode

0

0

SMBus and PWMI mode with DPST

VSC1

VSC0

OPERATION

0

X

No VSC error detection

1

0

VSC = 3.1V ±15%

1

1

VSC = 8V ±15%

OPERATION

ISL97635