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參數(shù)資料
| 型號： | AAT1239ITP-1-T1 |
| 廠商： | Advanced Analogic Technologies, Inc. |
| 英文描述： | 40V Step-Up Converter for 4 to 10 White LEDs |
| 中文描述： | 40V的升壓轉(zhuǎn)換器為4至10個白光LED |
| 文件頁數(shù)： | 17/21頁 |
| 文件大?。?/td> | 915K |
| 代理商： | AAT1239ITP-1-T1 |
AAT1239-1
40V Step-Up Converter for 4 to 10 White LEDs
SwitchReg
TM
PRODUCT DATASHEET
1239-1.2007.10.1.0
17
w w w . a n a l o g i c t e c h . c o m
The output inductor (L) is selected to avoid saturation at
minimum input voltage, maximum output load condi-
tions. Peak current may be estimated using the follow-
ing equation, assuming continuous conduction mode.
Worst-case peak current occurs at minimum input volt-
age (maximum duty cycle) and maximum load. Switching
frequency (F
S
) can be estimated from the curves and
assumes a 2.2
μ
H inductor.
I
OUT
(1 - D
MAX
)
D
MAX
·
V
IN(MIN)
(2
·
F
S
·
L)
I
PEAK
=
+
At light load and low output voltage, the controller
reduces the operating frequency to maintain maximum
operating efficiency. As a result, further reduction in
output load does not reduce the peak current. Minimum
peak current can be estimated from 0.5A to 0.75A.
At high load and high output voltages, the switching fre-
quency is somewhat diminished, resulting in higher I
PEAK
.
Bench measurements are recommended to confirm actu-
al I
PEAK
and ensure that the inductor does not saturate at
maximum LED current and minimum input voltage.
The RMS current flowing through the boost inductor is
equal to the DC plus AC ripple components. Under
worst-case RMS conditions, the current waveform is
critically continuous. The resulting RMS calculation yields
worst-case inductor loss. The RMS current value should
be compared against the manufacturer’s temperature
rise, or thermal derating, guidelines.
I
PEAK
I
RMS
=
3
For a given inductor type, smaller inductor size leads to
an increase in DCR winding resistance and, in most
cases, increased thermal impedance. Winding resistance
degrades boost converter efficiency and increases the
inductor’s operating temperature.
P
LOSS(INDUCTOR)
= I
RMS2
· DCR
To ensure high reliability, the inductor case temperature
should not exceed 100oC. In some cases, PCB heatsink-
ing applied to the LIN node (non-switching) can improve
the inductor’s thermal capability. PCB heatsinking may
degrade EMI performance when applied to the SW node
(switching) of the AAT1239-1.
Shielded inductors provide decreased EMI and may be
required in noise sensitive applications. Unshielded chip
inductors provide significant space savings at a reduced
cost compared to shielded (wound and gapped) induc-
tors. In general, chip-type inductors have increased
winding resistance (DCR) when compared to shielded,
wound varieties.
Inductor Efficiency Considerations
The efficiency for different inductors is shown in Figure 8
for ten white LEDs in series. Smaller inductors yield
increased DCR and reduced operating efficiency.
63
66
69
72
75
2
5
8
11
14
17
20
LED Current (mA)
E
CDRH5D16F-2R2 (29m
Ω
)
SD3814-2R2 (77m
Ω
)
Figure 8: AAT1239-1 Efficiency for
Different Inductor Types (V
IN
= 3.6V;
Ten White LEDs in Series).
Manufacturer
Sumida
www.sumida.com
Cooper Electronics
www.cooperet.com
Taiyo Yuden
www.t-yuden.com
Part Number
Inductance
(
μ
H)
Maximum DC I
SAT
Current (mA)
DCR
(m
Ω
)
Size (mm)
LxWxH
Type
CDRH2D14-2R2
2.2
1500
75
3.2x3.2x1.55
Shielded
SD3814-2R2
SD3110-2R2
NP03SB-2R0M
NR3010T-2R2M
2.2
2.2
2
2.2
1900
910
1900
1100
77
161
32
95
4.0x4.0x1.0
3.1x3.1x1.0
4.0x4.0x1.8
3.0x3.0x1.0
Shielded
Shielded
Shielded
Shielded
Table 4: Recommended Inductors for Various Output Levels (Select I
PEAK
< I
SAT
).
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