PRODUCT DATASHEET
AAT2861
TM
ChargePump
Backlight/Flash LED Driver and Multiple LDO Lighting Management Unit
Address
Data
THI
TLAT
TLO
TLAT
EN/SET
Address
1
2
17
18
1
2 . . .
n <= 16
0
1
0
0
n
Data Reg 1
Data Reg 2
Figure 1: AS2Cwire Serial Interface Timing Diagram.
AS2Cwire latches data or address after the EN/SET input
has been held high for time tLAT (500μs). Address or data
is differentiated by the number of EN/SET rising edges.
Since the data registers are 4 bits each, the differentiating
number of pulses is 24 or 16, so that Address 0 is identi-
fied by 17 rising edges, Address 1 by 18 rising edges,
Address 2 by 19 rising edges, etc. Data is set to any num-
ber of rising edges between 1 and 16. A typical write
protocol is a burst of EN/SET rising edges identifying a
particular address, followed by a pause with EN/SET held
high for the tLAT timeout period, then a burst of rising
edges signifying data, and another tLAT timeout after the
data has been sent. Once an address is set, multiple
writes to that address are allowed since the address is not
reset after each write. Address edges are needed when
changing the address, or writing to an address other than
the default after shutdown. Address 0 is the default
address after shutdown. If the part is enabled with only
data edges and no address, then Address 0 will be pro-
grammed and LED Backlight channels BL1-BL7 will be
enabled according to the number of data edges applied.
Backlight Current Control (Address 0)
Address 0 controls the enabling of the Main and Sub
channels. Table 2 shows the Data Codes used to control
the Main and Sub Channels independently. The default
condition for all backlight outputs (BL1-BL7) is OFF after
power-up.
The AAT2861 family of LMUs also provides an internal LED
current fade-in, fade-out feature. This feature is useful in
those applications where it is preferred to turn on and off
the backlight current using a smooth transition versus an
abrupt transition. During the fade-in cycle, the LED cur-
rent will be slowly increased to the programmed current
level (set in Addresses 2 to 5). During the fade-out cycle,
the LED current will be decreased linearly down to its
programmed fade-out current threshold (set by Address
1) at which point the BL channels will be turned off. The
fade-in and fade-out current is a linear transition over a
time period of approximately 1 second.
The fade-in and fade-out function can be enabled and
disabled independently for the Main and Sub groups by
writing the desired Data to Address 0. Table 2 also lists
the data codes used to program enable and disable the
fade functions for the main and sub channels. If the
“Main Equals Sub” feature (Address 3) is enabled
(MEQS=1), the fade-in and fade-out settings for the Main
and Sub channels are controlled by the “Main Fade” set-
ting and the “Sub Fade” bit in Address 1 will be ignored.
When EN/SET is held low for a time longer than tOFF
(500μs), the AAT2861 enters shutdown mode and draws
less than 1μA of current from IN. At shutdown, the data
and address registers are reset to 0.
AS2Cwire Serial Interface Programming
The AAT2861’s AS2Cwire programmable Address regis-
ters are listed in Table 1. There are 14 Address registers,
four registers control the three LDOs, six control the
backlight LED configuration, two control the flash/lamp
LED configuration and two are used to individually dis-
able each backlight or flash channel.
At startup when the EN/SET pin is first pulled high,
Address 0 is the default active register. The main and
sub channels can be turned on by immediately writing
data. For example, if Data = 4 is written the main and
sub channels will turn on to the default value of 19mA.
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2861.2009.02.1.2
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
