AAT1401 Datasheet, PDF (13/19 Pages) List of Unclassifed Manufacturers – FOUR-CHANNEL DIGITAL STILL CAMERA POWER SUPPLY

DATA SHEET
AAT1401
Serial LED Driver with Filtered PWM and 32-Step S2C Dimming Control
Considering the inductor copper loss, the inductor DCR
value together with the RMS current value flowing
through the inductor leads to inductor conduction loss
and also affects total efficiency. Larger DCR leads to
larger conduction loss and decreases total efficiency. The
inductor conduction loss can be estimated as shown in
the equation:
P_{L_LOSS}
=
I2
L_RMS
·
DCR
=
1
3
·
(I^2L_MAX
+
I2
L_MIN
+
I_{L_MAX}
·
I_{L_MIN})
·
DCR
I_{L_MAX} and I_{L_MIN} are the inductor peak current and mini-
mum current. Figure 5 shows DCR effects on efficiency
with a 10µH inductor.
90
86
82
78
74
70
66
62
58
54
50
46
42
10µH DCR 235mΩ 3.2x3.2x1.55mm
38
10µH DCR164mΩ 4.0x4.0x2.0mm
34
10µH DCR 36mΩ 8.3x8.3x3.0mm
30
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
ILED (mA)
Figure 5: Inductor DCR Effects on
Total Efficiency with 10µH at 3.6V V_IN.
Inductor saturation current is also a key parameter in
selecting an inductor. For the step-up converter, the peak
inductor current is the DC input current plus half the
inductor peak-to-peak current ripple.
DC
input
current:
I_IN
=
V_OUT · I_LED
V_IN · η
Inductor peak-to-peak current ripple:
I_{L_PP}
=
V_IN · (V_OUT - V_IN)
V_OUT · L · f
Inductor peak current:
I_{L_PEAK} = I_IN +
I_{L_PP}
2
=
V_OUT · I_LED
V_IN · η
+
V_IN · (V_OUT
2 · V_OUT ·
- V_IN)
L·f
For example, for a white LED with 3.2V V_F and 20mA
current at 82% efficiency, the inductor peak current is
I_{L_PEAK}
=
3.2 · 6 · 0.02
3.6 · 0.82
+
3.6 · (3.2 · 6 - 3.6)
2 · 3.2 · 6 · 10µ · 1M
= 276mA
Table 5 gives some examples of recommended inductors
for use with the AAT1401.
OVP Setting
Over-voltage protection is designed to protect the step-up
converter from a LED string open fault. The OVP threshold
is 1.2V. For 6 white LEDs with V_F up to 4V, the resistor
divider values for R1 and R2 can be calculated by:
R₁ =
V_OUT
V_{OVP_TH}
-
1
· R₂
Higher resistor divider values decrease the power loss on
the resistors. The total resistor value for 24V V_OUT should
be less than 2.4MΩ for better noise immunity. Values of
1MΩ for resistor R1 and 51kΩ for resistor R2 are recom-
mended.
Manufacturer
Sumida
Murata
Coilcraft
Coiltronics
Part Number
CDRH3D18-100
CDRH3D23-220
LQH44PN100MP0L
LQH44PN220MP0L
EPL2014-103MLC
LPS4012-223MLC
SD18-100-R
Inductance
(µH)
10
22
10
22
10
22
10
Maximum DC I_SAT
Current (mA)
900
550
1150
800
600
790
982
DCR
(mΩ, typ)
164
219
160
370
440
600
158
Size (mm)
LxWxH
4.0x4.0x2.0
3.9x3.9x2.5
4.0x4.0x1.65
4.0x4.0x1.65
2.1x2.2x1.0
4.1x4.1x1.2
5.8x5.8x1.8
Type
Shielded
Shielded
Non-shielded
Non-shielded
Shielded
Shielded
Shielded
Table 5: Example of AAT1401 Inductor Selection.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012
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