AAT2803ISK-4.5-T1 AnalogicTech, AAT2803ISK-4.5-T1 Datasheet - Page 12

• Manufacturer Part Number: AAT2803ISK-4.5-T1
• Description: Six-Channel White LED Backlight Charge Pump with Flash
• Manufacturer: AnalogicTech

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
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.
12
Data
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
Table 1: Current Level Settings.
30mA Max
I
OUT
30.0
26.7
23.8
21.4
19.0
16.7
15.2
13.3
10.5
11.9
9.5
8.6
7.6
6.7
6.2
0.0
(mA)
20mA Max
I
OUT
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
(mA)
F
) for the LED being
15mA Max
I
OUT
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
(mA)
AS
The Advanced Simple Serial Control (AS
single wire interface is used to set the possible
combinations of current levels and LED channel
states. AS
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.
AS
the EN/SET pin to address and load the registers.
AS
EN/SET pin has been held high for time T
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
2
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
ing edges signifying Data, and a T
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
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.
4
or 16, so that Address 1 is signified by 17 rising
2
Six-Channel White LED Backlight
2
2
Cwire relies on the number of rising edges of
Cwire latches data or address after the
Cwire Serial Interface
2
Cwire has addressing capability for
Charge Pump with Flash
OFF
LAT
, the backlight charge pump
timeout period, a burst of ris-
LAT
2803.2006.04.1.5
timeout for
2
Cwire)
LAT
.