AAT1239-1_0810 Datasheet, PDF (15/23 Pages) Advanced Analogic Technologies – 40V Step-Up Converter for 4 to 10 White LEDs

SwitchReg^TM
PRODUCT DATASHEET
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
Rising Clock
Edges/Data
Register
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
SEL = Low
Reference
Voltage (V)
0.4 (default)
0.38
0.36
0.34
0.32
0.30
0.28
0.26
0.24
0.22
0.20
0.18
0.16
0.14
0.12
0.10
LED Current (mA);
R_BALLAST = 30.1Ω
13.29
12.62
11.96
11.30
10.63
9.97
9.30
8.64
7.97
7.31
6.64
5.98
5.32
4.65
3.99
3.32
SEL = High
Reference
Voltage (V)
0.6 (default)
0.58
0.56
0.54
0.52
0.50
0.48
0.46
0.44
0.42
0.40
0.38
0.36
0.34
0.32
0.30
LED Current (mA);
R_BALLAST = 30.1Ω
19.93
19.27
18.60
17.94
17.28
16.61
15.95
15.28
14.62
13.95
13.29
12.62
11.96
11.30
10.63
9.97
Table 2: AAT1239-1 S²Cwire Reference Feedback Voltage Control Settings With R_BALLAST = 30.1Ω
(Assumes Nominal Values)*.
Selecting the Schottky Diode
To ensure minimum forward voltage drop and no recov-
ery, high voltage Schottky diodes are considered the
best choice for the AAT1239-1 boost converter. The out-
put diode is sized to maintain acceptable efficiency and
reasonable operating junction temperature under full
load operating conditions. Forward voltage (V_F) and
package thermal resistance (θ_JA) are the dominant fac-
tors to consider in selecting a diode. The diode non-re-
petitive peak forward surge current rating (I_FSM) should
be considered for high pulsed load applications, such as
camera flash. I_FSM rating drops with increasing conduc-
tion period. Manufacturers’ datasheets should be con-
sulted to verify reliability under peak loading conditions.
The diode’s published current rating may not reflect
actual operating conditions and should be used only as a
comparative measure between similarly rated devices.
40V rated Schottky diodes are recommended for outputs
less than 30V, while 60V rated Schottky diodes are rec-
ommended for outputs greater than 35V.
The switching period is divided between ON and OFF
time intervals.
1
F_S
=
T_ON
+
T_OFF
During the ON time, the N-channel power MOSFET is
conducting and storing energy in the boost inductor.
During the OFF time, the N-channel power MOSFET is
not conducting. Stored energy is transferred from the
input battery and boost inductor to the output load
through the output diode.
Duty cycle is defined as the ON time divided by the total
switching interval.
D
=
T_ON
T_ON + T_OFF
= T_ON ⋅ F_S
*All table entries are preliminary and subject to change without notice.
1239-1.2008.10.1.2
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