AAT3131ITP-T1 View Datasheet(PDF) - Advanced Analogic Technologies
Part Name
Description
MFG CO.
AAT3131ITP-T1
Advanced Analogic Technologies
'AAT3131ITP-T1' PDF : 14 Pages View PDF
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
up such that outputs D1-D3 can be controlled inde-
pendently of output D4. For addresses 1 to 8, 9 to
16, 17 to 24, and 25 to 32, outputs D1-D3 start at
0mA and increase from 0.5mA to 20mA in three
8dB steps and three 2.5dB steps. Output D4
remains constant over these address ranges which
provides orthogonal control of the two channels.
For addresses 1 to 8, D4 is set to 0mA. For
addresses 9 to 16, D4 is set to 1mA. For address-
es 17 to 24, D4 is set to 15mA, and for addresses
25 to 32, D4 is set to 30mA. This is summarized in
Table and Figure 1.
The modulo 32 interface wraps states back to state
1 after the 32nd clock. With each EN/SET pulse,
the output current changes to the next setting in the
address decoding. To change settings to the previ-
ous address decoding, 31 EN/SET clock pulses
are required. The counter can be clocked at
speeds up to 1MHz, so intermediate states are not
visible. The first rising edge of EN/SET enables the
IC and initially sets the output LED currents 0mA.
Additional clocks are required to set the desired
current level. Once the final clock cycle is input for
the desired brightness level, the EN/SET pin is held
high to maintain the device output current at the
programmed level. The device is disabled 500µs
after the EN/SET pin transitions to a logic low state.
Applications Information
Constant Current Output Level Settings
The constant current source output amplitude for
output D1 to D3 and D4 are set via the serial inter-
face according to a logarithmic scale described in
the following chart and the previous section. Using
a logarithmic scale, LED brightness appears linear
with each increasing code count. Because the out-
puts D1 to D4 are true independent constant cur-
rent sources, the voltage observed on any single
given output will be determined by the actual for-
ward voltage (VF) for the LED being driven.
Since the output current of the AAT3131 is program-
mable through its simple serial control (S2Cwire™),
no PWM (pulse width modulation) or additional con-
trol circuitry is needed to control LED brightness.
This feature greatly reduces the burden on a micro-
controller or system IC to manage LED or display
brightness, allowing the user to "set it, and forget it."
Furthermore, with its high speed serial interface
(1MHz data rate), the output current of the AAT3131
can changed successively to brighten or dim LEDs,
in smooth transitions (e.g. to fade-out) or in abrupt
steps, giving the user complete programmability and
real time control of LED brightness.
30
25
20
15
10
5
0
8
Output Current Level Settings
Address Code
Figure 1.
3131.2004.08.1.1
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