AAT1239-1_0810 Datasheet, PDF (17/23 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
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 2.2μH inductor.
I_PEAK =
I_OUT
(1 - D_MAX)
+
D_MAX · V_IN(MIN)
(2 · F_S · L)
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_RMS =
I_PEAK
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.
Manufacturer
Sumida
www.sumida.com
Cooper Electronics
www.cooperet.com
Taiyo Yuden
www.t-yuden.com
Part Number
CDRH2D14-2R2
CDRH2D14-4R7
CDRH4D22/HP-4R7
CDRH3D18-100NC
SD3814-2R2
SD3110-2R2
SD3118-4R7
SD3118-100
NP03SB-2R0M
NR3010T-2R2M
NP03SB4R7
NP03SB100M
Inductance
(μH)
2.2
4.7
4.7
10
2.2
2.2
4.7
10
2
2.2
4.7
10
Maximum DC I_SAT
Current (mA)
1500
1000
2200
900
1900
910
1020
900
1900
1100
1200
800
DCR
(mΩ)
75
135
66
164
77
161
162
295
32
95
47
100
Size (mm)
LxWxH
3.2x3.2x1.55
3.2x3.2x1.55
5.0x5.0x2.4
4.0x4.0x2.0
4.0x4.0x1.0
3.1x3.1x1.0
3.1x3.1x1.8
3.1x3.1x1.8
4.0x4.0x1.8
3.0x3.0x1.0
4.0x4.0x1.8
4.0x4.0x1.8
Type
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Table 4: Recommended Inductors for Various Output Levels (Select I_PEAK < I_SAT).
1239-1.2008.10.1.2
www.analogictech.com
17