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參數(shù)資料
| 型號(hào)： | AAT1231ITP-1-T1 |
| 廠商： | Advanced Analog Technology,lnc. |
| 英文描述： | Step-Up DC/DC Converters for White LED Backlight Applications |
| 中文描述： | 升壓型DC / DC轉(zhuǎn)換器，用于白光LED背光應(yīng)用 |
| 文件頁數(shù)： | 13/27頁 |
| 文件大?。?/td> | 1535K |
| 代理商： | AAT1231ITP-1-T1 |
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AAT1231/1231-1
Step-Up DC/DC Converters for
White LED Backlight Applications
1231.2007.01.1.2
13
V
F
= Schottky Diode DS1 forward voltage at turn-
OFF
V
RING
= Voltage ring occurring at turn-OFF
LED Selection and Current Setting
The AAT1231/1231-1 are well suited for driving
white LEDs with constant current. Applications
include main and sub-LCD display backlighting,
and color LEDs.
The LED current is controlled by the FB voltage
and the ballast resistor. For maximum accuracy, a
1% tolerance resistor is recommended.
The ballast resistor (R
BALLAST
) value can be cal-
culated as follows:
where:
V
FB(MAX)
= 0.4V when SEL = Low
V
FB(MAX)
= 0.6V when SEL = High
i.e., for a maximum LED current of 20mA (SEL =
High):
Table 1: Maximum LED Current and R
BALLAST
Resistor Values (1% Resistor Tolerance).
Typical white LEDs are driven at maximum con-
tinuous currents of 15mA to 20mA. For maximum
output, two parallel strings of six series LEDs are
used. A total output current of 30mA or 40mA is
required (15mA to 20mA in each string). The
maximum quantity of series connected LEDs is
determined by the minimum OVP voltage of the
boost converter (V
OUT(OVP_MIN)
), minus the maxi-
mum feedback voltage (V
FB(MAX)
) divided by the
maximum LED forward voltage (V
FLED(MAX)
).
V
FLED(MAX)
can be estimated from the manufactur-
ers’ datasheet at the maximum LED operating
current.
Figure 4 shows the schematic of using six LEDs in
series. Assume V
FLED
@ 20mA = 3.5V (typical)
from LW M673 (OSRAM) datasheet.
Therefore, under typical operating conditions, six
LEDs can be used in series.
21.82V
- 0.6V
3.5V
N =
≈
6.1
·
+ 1
V
OUT(OVP_MIN)
= 1.1V
= 21.82V
226k
Ω
12k
Ω
(V
OUT(OVP_MIN)
- V
FB(MAX)
)
V
FLED(MAX)
N =
·
+ 1
V
OUT(OVP_MIN)
= V
OVP(MIN)
R
2
R
3
Maximum I
Current (mA)
R
BALLAST
(
Ω
)
SEL = High
SEL = Low
50
40
35
30
25
20
15
10
5
12.1
15.0
16.9
20.0
24.3
30.1
40.2
60.4
121.0
8.06
10.0
11.3
13.3
16.2
20.0
26.7
40.2
80.6
V
FB
I
LED(MAX)
0.6
0.020
R
BALLAST
=
=
= 30
Ω
≈
30.1
Ω
V
FB(MAX)
I
LED(MAX)
R
BALLAST
=
·
+ 1
+ V
F
+ V
RING
V
SW(MAX)
= V
OVP(MAX)
R
3
R
2
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