AAT3132/32A
High Efficiency 1.5X Fractional Charge
Pump for White LED Applications
rent source output magnitude is controlled by the
EN/SET serial data interface. The interface
records rising edges of the EN/SET pin and
decodes them into 32 addresses corresponding to
individual current level settings. The 32 address-
es are divided up such that outputs D1 to D3 can
be controlled independently of output D4. For
Addresses 1 to 8, 9 to 16, 17 to 24, and 25 to 32,
outputs D1 to 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 the next brightness setting; likewise for
Addresses 17 to 24 and Addresses 25 to 32. This
is summarized in Table 1 and Figure 1.
The modulo 32 interface wraps 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
previous 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.
30
25
20
Current (mA)
15
10
5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Address Code
Figure 1: Output Current Level Settings (Option AAT3132).
8
3132.2005.12.1.4
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
