AAT1138 Datasheet, PDF (18/21 Pages) Skyworks Solutions Inc. – 2A Step-Down Converter with Adjustable Input Current Limit

DATA SHEET
AAT1138
2A Step-Down Converter with Adjustable Input Current Limit
Layout Guidance
When laying out the PC board, the following layout
guidelines should be followed to ensure proper operation
of the AAT1138:
1. The exposed pad (EP) must be reliably soldered to
the GND plane. A GND pad below EP is strongly rec-
ommended.
2. The power traces, including the GND trace, the SW
trace and the SYSIN, SYSOUT trace should be kept
short, direct and wide to allow large current flow.
The L1 connection to the SW pins should be as short
as possible. Do not put any signal lines under the
inductor.
3. The input capacitor (C1 and C21) should connect as
closely as possible to SYSIN and SYSOUT and GND
to get good power filtering.
4. Keep the switching node, SW away from the sensi-
tive FB node.
5. The feedback trace should be separate from any
power trace and connect as closely as possible to the
load point. Sensing along a high-current load trace
will degrade DC load regulation. External feedback
resistors should be placed as closely as possible to
the FB pin to minimize the length of the high imped-
ance feedback trace.
6. The resistance of the trace from the load return to
GND should be kept to a minimum. This will help to
minimize any error in DC regulation due to differ-
ences in the potential of the internal signal ground
and the power ground.
VOUT
R2
SYSOUT
59k
C32
330μF
C4
R1
SW
100pF 316k ^L1
2.2μH
C31
22μF
VIN
C1
1μF
U1
AAT1138
1 _GND
FB
2 _SW
GND
3 _SW
SVIN
4 _PGND
PVIN
5 _PGND
ENBUCK
6 _{GND EP SYSOUT}
7 _SYSIN
SYSOUT
8 _ENSYS
SET
ENSYS
16
15 GND
14
13
12
11
10
9
C21
22μF
RSET
11.5k
C22 C23 C24 C25
330μF 330μF 330μF 330μF
ENBUCK
Figure 3: AAT1138 Evaluation Board Schematic.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
18
201978B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013