ISL97635 datasheet(21/28 Pages) INTERSIL

21 / 28 page

FN6434.2

December 22, 2008

• When an SMBus mode is selected, Register 0x00 reflects

the last value written to it. But, when any non-SMBus

mode is selected, Register 0x00 reflects the current

brightness value based on the current mode of operation,

with the exception of SMBus mode with DPST, where

PWM_MD = 0 and PWM_SEL = 0.

• When SMBus mode with DPST is selected, Register 0x00

reflects the last value written to it from SMBus.

• When a write to Register 0x01 (Device Control Register)

causes the backlight controller to transition to an SMBus

mode, the brightness of the BL does not change. On the

other hand, when a write to Register 0x01causes the

backlight controller to transition to a non-SMBus mode,

the brightness of the BL changes as appropriate for the

new mode.

• The default value for Register 0x01 is 0x00.

Fault/Status Register (0x02)

This register has 6 status bits that allow monitoring of the

backlight controller’s operating state. Bit 0 is a logical “OR” of all

fault codes to simplify error detection. Not all of the bits in this

The remaining bits are reserved and return a “0” when read and

ignore the bit value when written. All of the bits in this register

are read-only, with the exception of bit 0, which can be cleared

by writing to it.

• A Read Byte cycle to Register 0x02 indicates the current

BL on/off status in BL_STAT (1 if the BL is on, 0 if the BL is

off).

• A Read Byte cycles to Register 0x2 also returns FAULT as

the logical OR of THRM_SHDN, OV_CURR, 2_CH_SD,

and 1_CH_SD should these events occur.

• 1_CH_SD returns a 1 if one or more channels have

faulted out.

• 2_CH_SD returns a 1 if two or more channels have faulted

out.

• A fault will not be reported in the event that the BL is

commanded on and then immediately off by the system.

• When FAULT is set to 1, it will remain at 1 even if the

signal which sets it goes away. FAULT will be cleared

when the BL_CTL bit of the Device Control Register is

toggled or when written low. At that time, if the fault

condition is still present or reoccurs, FAULT will be set to 1

again. BL_STAT will not cause FAULT to be set

• The controller will not indicate a fault if the VBL+ goes

away, whether or not the LEDs were on at the time of the

power loss. This can occur if there is some hang condition

that causes the user to force the system off by holding the

power button down for 4s.

• The default value for Register 0x02 is 0x00.

Identification Register (0x03)

The ID register contains 3-bit fields to denote the LED driver

(always set to 1), manufacturer and the silicon revision of the

controller IC. The bit field widths allow up to 16 vendors with up

to 8 silicon revisions each. In order to keep the number of

silicon revisions low, the revision field will not be updated unless

the part will make it out to the user’s factory. Thus, if during the

engineering development process, 3 silicon spins were

needed, the next available revision ID would be used for all 3

spins until that same ID made it to the factory. Except Bit 7,

which has to be 1, all of the bits in this register are read-only.

• Vendor ID 9 represents Intersil Corporation.

• The default value for Register 0x03 is 0xC8.

The initial value of REV shall be 0. Subsequent values of

REV will increment by 1.

ISL97635

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