AAT1235 Datasheet, PDF (11/21 Pages) Advanced Analogic Technologies – High Efficiency White LED Drivers for Backlight and Keypad

AAT1235
High Efficiency White LED Drivers
for Backlight and Keypad
Constant Current Output Level Settings
and AS²Cwire Serial Interface
The LED current sink level of each group and the
on/off status of each channel is controlled by
AnalogicTech's AS²Cwire serial digital input. Since
each current sink is programmable, no PWM or
additional control circuitry is needed to control LED
brightness. This feature greatly reduces the burden
on a microcontroller or system IC to manage LED
or display brightness, allowing the user to "set it
and forget it." With its high-speed serial interface
(1MHz data rate), the input sink current can be
changed quickly and easily. Also the non-pulsating
LED current reduces system noise and improves
LED reliability.
AS²Cwire relies on the number of rising edges of
the EN/SET pin to address and load the registers.
AS²Cwire latches data or address after the EN/SET
pin has been held high for time T_LAT (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 signified by 17 rising
edges, Address 1 by 18 rising edges, and so forth.
Data is set to any number of rising edges between
1 and including 16. A typical write protocol is a
burst of EN/SET rising edges, signifying a particu-
lar address, followed by a pause with EN/SET held
high for the T_LAT timeout period, a burst of rising
edges signifying data, and a T_LAT timeout for the
data registers. Once an address is set, then multi-
ple writes to that address are allowed where only
data is issued. When EN/SET is held low for an
amount of time longer than T_OFF (500µs), the
AAT1235 enters into shutdown mode and draws
less than 1µA from the input. Data and Address
registers are cleared (reset to 0) during shutdown.
Address
0
1
2
3
4
EN/SET
Rising Edges
17
18
19
20
21
Data
Register
B1-B2 current
A1-A3 current
B1-B2 on/off
A1-A3 on/off
A1-A3, B1-B2 on
Table 1: AS²Cwire Serial Interface Addressing.
Address 0 and 1: LED Brightness Control
Outputs A1, A2, A3, B1, B2 are each capable of
sinking up to 30mA. The maximum current can be
programmed by an external resistor at the RSET
pin. It is suggested to connect up to four white
LEDs in series for each channel and to keep the
same number of LEDs in each channel.
Outputs B1 and B2 are intended to drive the white
LEDs for the backlight in a phone, while A1:A3 can
supply the keypad LEDs. For large displays, all five
outputs can be used.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
All Outputs (%)
100
84
71
60
51
43
35
31
26
21
18
15
13.5
12.0
10.5
9.0
Table 2: Address 0 and 1 for Current Setting as
Percentage of the Maximum Level Set by R_SET.
Address 2: LED Group B ON/OFF
Control
Data
B1
B2
1
Off
Off
2
Off
On
3
On
Off
4
On
On
Table 3: Address 2 for Group B ON/OFF State.
1235.2007.02.1.1
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