AAT2803 Datasheet, PDF (12/16 Pages) Advanced Analogic Technologies – Six-Channel White LED Backlight Charge Pump with Flash

Constant Current Output Level Settings
The constant current sink levels for the white LED
backlight (D1 to D6) are set via the serial interface
according to a logarithmic scale where each code is
1dB lower than the previous code. In this manner,
LED brightness appears linear with each increasing
code count. Because the inputs D1 to D6 are true
independent constant current sinks, the voltage
observed on any single given input will be determined
by the actual forward voltage (V_F) for the LED being
driven.
Since the input current sinks are programmable, no
PWM (pulse width modulation) or additional control
circuitry is needed to control LED brightness. This fea-
ture 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 successively to brighten or
dim LEDs in smooth transitions (e.g., to fade-out) or in
abrupt steps, giving the user complete programmabil-
ity and real-time control of LED brightness.
The 16 individual current level settings are each
approximately 1dB apart (see Current Level Settings
table). Code 1 is full scale, Code 15 is full scale atten-
uated by 14dB, and Code 16 is reserved as a "no cur-
rent" setting.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
30mA Max
I_OUT (mA)
30.0
26.7
23.8
21.4
19.0
16.7
15.2
13.3
11.9
10.5
9.5
8.6
7.6
6.7
6.2
0.0
20mA Max
I_OUT (mA)
20.0
17.8
15.9
14.3
12.7
11.1
10.2
8.9
7.9
7.0
6.3
5.7
5.1
4.4
4.1
0.0
15mA Max
I_OUT (mA)
15.0
13.3
11.9
10.7
9.5
8.3
7.6
6.7
6.0
5.2
4.8
4.3
3.8
3.3
3.1
0.0
Table 1: Current Level Settings.
12
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
AS²Cwire Serial Interface
The Advanced Simple Serial Control (AS²Cwire)
single wire interface is used to set the possible
combinations of current levels and LED channel
states. AS²Cwire has addressing capability for
multiple data registers. With multiple data regis-
ters, the backlight charge pump main and sub-
channels can be programmed together or inde-
pendently from one another.
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.
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 1 is signified by 17 rising
edges, Address 2 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 partic-
ular Address, followed by a pause with EN/SET
held high for the T_LAT timeout period, a burst of ris-
ing edges signifying Data, and a T_LAT timeout for
the data registers. Once an address is set, then
multiple writes to the corresponding data register
are allowed.
When EN/SET is held low for an amount of time
greater than T_OFF, the backlight charge pump
enters into shutdown mode and draws less than
1μA from the supply. Address 1 is the default
address on the first rising edge after the backlight
charge pump has been disabled. Whenever shut-
down mode is entered, all registers are reset to 1.
2803.2006.12.1.6