AAT1239-1_0810 Datasheet, PDF (14/23 Pages) Advanced Analogic Technologies – 40V Step-Up Converter for 4 to 10 White LEDs

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PRODUCT DATASHEET
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
Alternatively, toggling the SEL logic pin from low to high
implements stepped or pulsed LED currents by increas-
ing the FB pin voltage. Figure 6 illustrates the SELECT
pin scaling factor, defined as the LED current with
SEL=HIGH divided by the LED current with SEL=LOW. In
the AAT1239-1, the possible scaling factors are 3.0x to
1.5x with the internal default setting of 1.5x.
3. 5
3. 0
2. 5
2. 0
(Default)
1. 5
1. 0
1
4
7
10
13
16
S²Cwire Data Register
Figure 6: AAT1239-1 SEL Pin Scaling Factor:
I_LED (SEL = High) Divided by I_LED (SEL = Low).
S²Cwire Serial Interface
AnalogicTech’s S²Cwire single wire serial interface is a
proprietary high-speed single-wire interface available
only from AnalogicTech. The S²Cwire interface records
rising edges of the EN/SET input and decodes them into
16 individual states. Each state corresponds to a refer-
ence feedback voltage setting on the FB pin, as shown in
Table 2.
S²Cwire Serial Interface Timing
The S²Cwire single wire serial interface data can be
clocked-in at speeds up to 1MHz. After data has been
submitted, EN/SET is held high to latch the data for a
period T_LAT. The FB pin voltage is subsequently changed
to the level as defined by the state of the SEL logic pin.
When EN/SET is set low for a time greater than T_OFF, the
AAT1239-1 is disabled. When the AAT1239-1 is disabled,
the register is reset to its default value. In the AAT1239-1,
the FB pin voltage is set to 0.3V if the EN/SET pin is
subsequently pulled HIGH.
S²Cwire Feedback Voltage Programming
The FB pin voltage is set to the default level at initial
powerup. The AAT1239-1 is programmed through the
S2Cwire interface. Table 2 illustrates FB pin voltage pro-
gramming for the AAT1239-1. The rising clock edges
applied at the EN/SET pin determine the FB pin voltage.
If a logic LOW is applied at the SEL pin of the AAT1239-1,
the default feedback voltage range becomes 0.4V to
0.1V and 0.6V to 0.3V for a logic HIGH condition at the
SEL pin.
EN/SET
Data Reg
T_HI
T_LO
T _LAT
1
2
n-1
n ≤ 16
0
TOFF
n-1
0
Figure 7: AAT1239-1 S²Cwire Timing Diagram to Program the Output Voltage.
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1239-1.2008.10.1.2