AAT2612 Datasheet, PDF (14/18 Pages) Skyworks Solutions Inc. – Step-Down DC/DC Converter With Three High PSRR LDOs

DATA SHEET
AAT2612
Step-Down DC/DC Converter With Three High PSRR LDOs
Layout Considerations
The suggested PCB layout for the AAT2612 is shown in
Figures 2(a) - 2(d). The following guidelines are recom-
mended to ensure a proper layout:
1. Connect the input capacitors (C1, C2, C3) and out-
put capacitors (C5, C6, C7, C8 ) as close as possible
to the pins (INL1, INL2, INBK, VOUT) and power
ground (AGND, PGND) to minimize any parasitic
inductance in the switched current path which gen-
erates a large voltage spike during the switching
interval.
2. Keep the power traces (GND, LX, and INBK) short,
direct, and wide to allow large current flow. Place
sufficient multiple-layer pads when needed to change
the trace layer.
3. Connect the output capacitor C8 and inductor L1 as
close as possible to the device. Keep the connection
of L1 to the LX pins as short as possible and route
no signal lines under the inductor.
4. Separate the feedback traces or FB pin (Pin 9) from
any power trace and connect as close as possible to
the load point. Sensing along a high-current load
trace will degrade DC load regulation.
5. Keep the resistance of the trace from the load
returns to PGND 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.
6. Connect the ground pin of the exposed pad to AGND
internal plane with multiple vias to decrease the
effect of large power ground PGND noise on the ana-
log ground.
7. Connect the ground pins of LDO output capacitors to
AGND.
INL1
2.5V to 5.5V
INL2
2.5V to 5.5V
INBK
2.5V to 5.5V
C1
2.2μF
J_IN1
C2
2.2μF
J_IN2
C3
4.7μF
U1
AAT2612
1 _INL1
16 _INL2
4 _INBK
ENBK 7
ENBK
2
ENL1 _{ENL1 3}
ENL2 _{ENL2 11}
ENL3 _{ENL3 12}
13
AGND
17
ENBK
N/C
ENL1
ENL2
ENL3
AGND
AGND
OUTL1 ²⁰
LDO1
C5
1μF
LDO1
OUTL2 ¹⁵
LDO2
C6
1μF
LDO2
OUTL3 ¹⁴
LDO3
C7
1μF
LX ⁵
FB ⁹
PGND ⁶
LX
FB
PGND
L1
2.2μH
C4
N/C
R1
59k
LDO3
BO1
1.2V 600mA
C8
10μF
R2
59k
GND
Figure 1: AAT2612IDG Evaluation Board Schematic.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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202407B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 20, 2013