AAT3134
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Current Level Settings (mA)
D1 to D4
D5 to D6
0
1
10
12
15
20
0
1
10
12
15
20
0
1
10
12
15
20
0
1
10
12
15
20
0
1
10
12
15
20
0
20
0
0
0
0
0
0
1
1
1
1
1
1
10
10
10
10
10
10
12
12
12
12
12
12
15
15
15
15
15
15
20
20
EN/SET Serial Interface
The current source output magnitude is controlled
by the EN/SET serial interface. The interface
records rising edges of the EN/SET pin and
decodes them into 32 individual current level set-
tings, as summarized in Table 1. The modulo 32
interface wraps back to State 1 after the 32nd
clock, so that the previous state is achieved by
clocking the EN/SET pin 31 times. The counter can
be clocked at speeds up to 1MHz, so that interme-
diate states are not visible. The first rising edge of
EN/SET enables the IC and initially sets the output
LED current to 0. 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. The EN/SET timing is designed to
accommodate a wide range of data rates. After the
first rising edge of EN/SET, the charge pump is
enabled and reaches full capacity after the soft-
start time (T
SS
). During the soft-start time, multiple
clock pulses may be entered on the EN/SET pin to
set the final output current level with a single burst
of clocks. Alternatively, the EN/SET clock pulses
may be entered one at a time to gradually increase
the LED brightness over any desired time period. A
constant current is sourced as long as EN/SET
remains in a logic high state. The current source
outputs are switched off after EN/SET has
remained in a low state for at least the T
OFF
timeout
period.
Address
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
Table 1: Constant Current Source Output
Programming Levels.
3134.2005.12.1.1
9
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
