AAT1401 Datasheet, PDF (12/19 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
Capacitor Selection
A compensation capacitor C_COM is used for step-up con-
verter loop compensation, soft startup time control, and
PWM digital signal filtering. Loop compensation requires
matching values for C_COM, C_OUT, I_LED, and V_OUT:
C_OUT
C_COM
<
30
·
I_LED
10^-6 ·
V_OUT
The AAT1401 can drive up to 6 white LEDs with forward
voltages up to 4V each. In a worst case with V_F of 4V, a
C_OUT value of 0.1µF, and LED maximum current of 20mA,
the value of C_COM should be higher than 3.6nF.
C_COM
>
C_OUT
· 30 ·
I_LED
V_OUT
(nF)
=
0.1
· 30
20
·
24
(nF)
=
3.6nF
A higher value for C_COM lengthens the soft startup time.
The relationship between C_COM and startup time is almost
linear, with startup time x 10⁵ magnification of C_COM; thus
56nF C_COM leads to a soft startup time of 5.6ms. Table 3
gives several examples of minimum C_COM values at differ-
ent C_OUT and I_LED and the step-up converter's operation
stable. Values of 56nF for C_COM and 0.1µF for C_OUT are
suitable in most cases.
I_LED (mA)
31
31
20
20
10
10
C_OUT (µF)
0.1
1
0.1
1
0.1
1
V_OUT (V)
24
24
24
24
24
24
C_{COM_MIN} (nF)
2.3
23
3.6
36
7.2
72
Table 3: Minimum C_COM Values vs. I_LED and C_OUT
(Step-Up Converter Operation Stable).
Multi-layer ceramic (MLC) capacitors provide small size
and adequate capacitance, low parasitic equivalent series
resistance (ESR) and equivalent series inductance (ESL),
and are well suited for use as input, output and compen-
sation capacitors in the AAT1401 step-up converter LED
driver application. MLC capacitors of type X7R or X5R are
recommended to ensure good capacitance stability over
the full operating temperature range. A 4.7µF/6.3V input
capacitor is recommended and a 0.1µF/50V output capac-
itor is suitable as noted above. Table 4 lists some recom-
mended capacitors for use with the AAT1401.
Inductor Selection
Inductor value, saturation current and DCR is most impor-
tant parameter in selecting an inductor for AAT1401.
The suitable inductance range for the AAT1401 is 4.7µH
to 22µH. Higher inductance lowers the step-up convert-
er's RMS current value. Together with lower DCR value
of the inductor, it makes the total inductor power loss
become much lower. Considering inductor size and cost,
10µH inductance is most suitable. Figure 4 illustrates
AAT1401 efficiency at different inductance with similar
DCR value.
90
86
82
78
74
70
66
62
58
54
50
46
42
4.7µH
38
10µH
34
22µH
30
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
ILED (mA)
Figure 4: AAT1401 Efficiency at Different
Inductance with Similar DCR (V_IN = 3.6V).
Manufacturer
Murata
Part Number
GRM188R60J475K
GRM188R71H104KA93
Value (µF)
4.7
0.1
Voltage (V)
6.3
50
Temperature Range
X5R
X7R
Table 4: Examples of AAT1401 Input and Output Capacitor Selection.
Case Size
0603
0603
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
12
202113A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 27, 2012