MAX8930
WLED Charge Pump, RGB, OLED Boost,
LDOs with ALC and CAI
WLED1–WLED8 Driver Operation
The white LED current regulators are composed of 4
main-group drivers (WLED1–WLED4) and 4 subgroup
drivers (WLED5–WLED8). The current of the main-group
LEDs can be selected by an I 2 C register. Both ambient
light control (ALC) mode and ramp-up/ramp-down con-
trol are applied to only the main-group white LEDs.
The subgroup LEDs can choose either individual control
or can belong to the main group based on the status
of a bit in the register (01h and 02h). In this function,
combinations can be adjusted as required. For example,
main 4ch + sub 4ch or main 5ch + sub 3ch.
The CAI (PWM) signal from either the LCD driver module
or baseband chipset controls only the main-group
WLEDS. The up/down slope control can be programmed
by the setting of the 0Ah register when the main LEDs
are controlled by either I 2 C or ALC.
For main LEDs, there are three different dimming control
methods, I 2 C, ALC, and CAI. The dimming range for
main LEDs and sub LEDs is from 0.1mA to 25.6mA in
0.1mA increments.
RGB Driver Operation
The brightness for each color LED has 256 different
steps (0.1mA to 25.6mA). The RGB LED can be activat-
ed by either the high/low status of the PLAY_ PWM signal
or by I 2 C ON/OFF command. The default dimming con-
trol is I 2 C command. An I 2 C command for dimming can
adjust the current of each RGB individually. The opera-
tion of ON/OFF by I 2 C command also allows individual
control. However, the operation of ON/OFF by PWM to
PLAY_ RGB is group control. To operate with either an
active-high or active-low signal coming from the micro-
processor such as audio processor, the register related
to active high or active low should be selected first (the
bit 1 in 20h). When a call comes in or music plays, all
RGB LEDs are allowed to be activated by either a PWM
signal applied to PLAY_ or a designated register by I 2 C.
The main purpose for the PLAY_ is for ON/OFF control
function and not for dimming control. If the dimming cur-
rent is set to 10mA on each RGB LED, the PWM signal
to PLAY_ RGB turns all of the current regulators on or off
at the same time. However, the dimming current for RGB
can be set by I 2 C command during ON/OFF operation.
When the PLAY_ is in active-high period, the RGB cur-
rent regulator is on with 10mA current. When the PLAY_
is in the opposite state (active-low period), the RGB
regulator is off with 0mA current. The default method to
turn the RGB LED on is to pull the PLAY_ input high with
Maxim Integrated
a minimum on-time of 80 F s in active-high mode. If bit 1
in 20h is set to 1, then all current regulators for RGB are
activated by active-low signal with a minimum off-time of
80 F s. The up/down slope control can be programmed by
the setting of the 0Bh register when the RGB LEDs are
controlled by I 2 C only.
If bit 7 in 20h is set to logic-low, then slope up/down is
automatically deactivated.
CAI (Contents Adaptive
Interface) Operation
A 200Hz PWM signal is applied to the CAI pin. The CAI
signal can be from either the LCD driver module with
gamma correction information or from the baseband
chipset. The main WLED can be activated by either
the high/low status of the CAI PWM signal or with either
an active-high or active-low signal coming from either
a LCD driver module or baseband chipset. The corre-
sponding register bit (bit 0 in 02h) should be set to either,
1 or 0 by I 2 C command.
Depending on the duty cycle, the brightness varies from
0mA to 25.6mA with the resolution of 0.256mA per 1%
duty variation. In control of CAI (PWM) independently, the
existing brightness setting from either I 2 C or ALC is over-
written because CAI has the priority over I 2 C and ALC.
See the Dimming by Digital PWM on CAI Only and
Dimming by Both Digital PWM on CAI and Either I 2 C or
ALC at the Same Time sections for details on the CAI
dimming control.
Dimming by Digital PWM on CAI Only
When the digital PWM (DPWM) signal (100Hz ~15kHz) is
provided by either the baseband or CPU for dimming the
brightness, the MAX8930 DPWM function takes over the
responsibility of dimming the main WLEDs. The dimming
by CAI is initiated by setting CAI (bit 7 of Register 02h)
to 1. After the set-up, both I 2 C register dimming settings
and ALC no longer control the dimming current for the
main WLEDs. The frequency range on the CAI pin is from
100Hz to 15kHz, where 0% duty cycle corresponds to
0mA and 100% duty cycle corresponds to full current,
25.6mA.
When CAI is set to 1, the ramp-up/down slope for main
WLED_ is automatically disabled by the MAX8930 con-
trol logic. Figure 3 is the timing diagram on initiating CAI.
The MAX8930 maintains its previous dimming setting
for t B (10ms typ) to allow the PWM filter time to settle to
its average value before activating CAI dimming. This
is done automatically inside the IC. The bit of MAINI2C
23