Rainbow Electronics MAX8759 - Manual (Page 23)

MAX8759
Low-Cost, SMBus, CCFL Backlight Controller
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BIT 7 BIT 6 BIT 5 (R/ W) BIT 4 (R/ W) BIT 3 (R/ W) BIT 2 (R/ W) BIT 1 (R/ W) BIT 0 (R/ W)
Reserved Reserved ALSDEL1 ALSDEL0 ALS_CTL PWM_MD PWM_SEL LAMP_CTL
ALSDEL1: ALS delay select bit.
ALSDEL0: ALS delay select bit.
ALS_CTL: Ambient-light-sensor select bit (1 = use ALS, 0 = not use ALS).
PWM_MD: PWM mode select bit (1 = absolute brightness, 0 = percentage change).
PWM_SEL: Brightness control select bit (1 = control by PWM, 0 = control by SMBus).
LAMP_CTL: Inverter on/off bit (1 = on, 0 = off).
A value of 1 written to LAMP_CTL turns on the lamp as
quickly as possible. A value of zero written to LAMP_CTL
immediately turns off the lamp.
The PWM_SEL bit determines whether the SMBus or
PWM input should control brightness when the inverter is
not in ALS mode. This bit has no effect when ALS_CTL is
set to 1.
The PWM_MD bit selects the manner in which the PWM
input is to be interpreted. When this bit is zero, the PWM
input reflects a percentage change in the current bright-
ness (i.e., DPST mode) and follows the following equation:
DPST brightness = BRT CURRENT
× D
PWM
where BRT CURRENT is the current brightness setting from
either ALS or SMBus without influence from the PWM
input and D
PWM is the duty cycle of the PWM signal.
When PWM_MD bit is 1, the PWM input has no effect on
the brightness setting unless the inverter is in PWM mode.
When ALS_CTL is 1, the inverter controls brightness
based primarily on the light reading from the ALS.
However, the ALS brightness setting can be modified if
the PWM_MD bit is set to zero. When the ALS_CTL bit
is zero, the inverter controls the brightness according
to the PWM input (PWM mode), the SMBus setting
(SMBus mode), or a combination of the two (SMBus
mode with DPST).
BIT 7 (R/
W)
BIT 6 (R/
W)
BIT 5 (R/
W)
BIT 4 (R/
W)
BIT 3 (R/
W)
BIT 2 (R/
W)
BIT 1 (R/
W)
BIT 0 (R/
W)
BRT7 BRT6 BRT5 BRT4 BRT3 BRT2 BRT1 BRT0
BRT[7..0]: 256 brightness levels.
Brightness Control Register [0x00]
(POR = 0xFF)
The brightness control register of the MAX8759 con-
tains 8 bits and supports 256 brightness levels. A write-
byte cycle to register 0x00 sets the brightness level if
the inverter is in SMBus mode. A write-byte cycle to
register 0x00 has no effect if the inverter is not in
SMBus mode. A read-byte cycle to register 0x00
returns the current brightness level regardless of the
operation mode. A setting of 0xFF for register 0x00 sets
the inverter to the maximum brightness. A setting of
0x00 for register 0x00 sets the inverter to the minimum
brightness.
Device Control Register [0x01] (POR = 0x00)
This register has a single bit that controls the inverter
ON/OFF state, 3 bits that control the operating mode of
the inverter, and 2 bits for setting ALS delay time. The
remaining bits are reserved for future use.