AAT1271 Datasheet, PDF (15/19 Pages) Advanced Analogic Technologies – 1.5A Step-Up Current Regulator for Flash LEDs

SwitchReg^TM
PRODUCT DATASHEET
AAT1271
1.5A Step-Up Current Regulator for Flash LEDs
Selecting the Boost Capacitors
In general, it is good design practice to place a decou-
pling capacitor (input capacitor) between the IN and GND
pins. An input capacitor in the range of 2.2μF to 10μF is
recommended. A larger input capacitor in this application
may be required for stability, transient response, and/or
ripple performance. The high output ripple inherent in
the boost converter necessitates the use of low imped-
ance output filtering. Multi-layer ceramic (MLC) capaci-
tors provide small size and adequate capacitance, low
parasitic equivalent series resistance (ESR) and equiva-
lent series inductance (ESL), and are well suited for use
with the AAT1271 boost regulator. MLC capacitors of type
X7R or X5R are recommended to ensure good capaci-
tance stability over the full operating temperature range.
The output capacitor is selected to maintain the output
load without significant voltage droop (∆V_OUT) during the
power switch ON interval. A 2.2μF ceramic output capac-
itor is recommended (see Table 7). Typically, 6.3V or 10V
rated capacitors are required for this flash LED boost
output. Ceramic capacitors selected as small as 0603 are
available which meet these requirements. MLC capacitors
exhibit significant capacitance reduction with applied
voltage. Output ripple measurements should confirm
that output voltage droop and operating stability are
within acceptable limits. Voltage derating can minimize
this factor, but results may vary with package size and
among specific manufacturers. To maintain stable opera-
tion at full load, the output capacitor should be selected
to maintain ∆V_OUT between 100mV and 200mV. The boost
converter input current flows during both ON and OFF
switching intervals. The input ripple current is less than
the output ripple and, as a result, less input capacitance
is required.
PCB Layout Guidelines
Boost converter performance can be adversely affected
by poor layout. Possible impact includes high input and
output voltage ripple, poor EMI performance, and
reduced operating efficiency. Every attempt should be
made to optimize the layout in order to minimize para-
sitic PCB effects (stray resistance, capacitance, and
inductance) and EMI coupling from the high frequency
SW node. A suggested PCB layout for the AAT1271 1.5A
step-up regulator is shown in Figures 3 and 4. The fol-
lowing PCB layout guidelines should be considered:
1. Minimize the distance from capacitor CIN and COUT’s
negative terminals to the PGND pins. This is espe-
cially true with output capacitor COUT, which conducts
high ripple current from the output to the PGND pins.
2. Minimize the distance under the inductor between IN
and switching pin SW; minimize the size of the PCB
area connected to the SW pin.
3. Maintain a ground plane and connect to the IC PGND
pin(s) as well as the PGND connections of C_IN and
C_OUT.
4. Consider additional PCB exposed area for the flash
LEDs to maximize heatsinking capability. This may
be necessary when using high current application
and long flash duration application.
5. Connect the exposed paddle (bottom of the die) to
either PGND or GND. Connect AGND, FLGND to GND
as close as possible to the package.
Manufacturer
Cooper Bussmann
Cooper Bussmann
Cooper Bussmann
Sumida
Coilcraft
Part Number
SD3812-1R0-R
SDH3812-1R0-R
SD10-1R0-R
CDH38D11/S
LPS4012-102NLC
Inductance
(μH)
1
1
1
1
1
Saturated Rated
Current (A)
2.69
3
2.25
2.8
2.5
DCR
(mΩ)
48
45
44.8
48.8
60
Size (mm)
LxWxH
4.0x4.0x1.2
3.8x3.8x1.2
5.2x5.2x1.0
4.0x4.0x1.2
4.1x4.1x1.2
Type
Shielded Drum Core
Shielded Drum Core
Shielded Drum Core
Shielded Drum Core
Shielded Drum Core
Table 6: Typical Suggested Surface Mount Inductors.
Manufacturer
Murata
Part Number
GRM185R60J225KE26
GRM188R71A225KE15
GRM21BR70J225KA01
GRM21BR71A225KA01
GRM219R61A475KE19
GRM21BR71A106KE51
Capacitance (μF)
2.2
2.2
2.2
2.2
4.7
10
Voltage Rating (V)
6.3
10
6.3
10
10
10
Temp Co.
X5R
X7R
X7R
X7R
X5R
X7R
Table 7: Typical Suggested Surface Mount Capacitors.
Case Size
0603
0603
0805
0805
0805
0805
1271.2008.08.1.1
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