AAT2148 Datasheet, PDF (13/18 Pages) Skyworks Solutions Inc. – Low-Noise, Fast Transient 1A Step-Down Converter

DATA SHEET
AAT2148
Low-Noise, Fast Transient 1A Step-Down Converter
Figure 2: AAT2148 Evaluation Board
Top Layer.
Figure 3: AAT2148 Evaluation Board
Bottom Layer.
VIN
VIN
C1
4.7µF
VIN
JP1
1
2
3
U1
AAT2148
12 _VP
LX ¹³
11 _VP
LX ¹⁴
10 _VP
LX ¹⁵
9 _VCC
EN 7 _EN
5 _N/C
6 _N/C
0 _EP
3 _PGND
FB ⁴
N/C ⁸
N/C ¹⁶
PGND ²
PGND ¹
L1 4.7µH
R1
267k
C3
100pF
VOUT
C2
10µF
R2
59k
Figure 4: AAT2148 Evaluation Board Schematic.
Adjustable Output Resistor Selection
For applications requiring an adjustable output voltage,
the 0.6V version can be externally programmed.
Resistors R1 and R2 of Figure 4 program the output to
regulate at a voltage higher than 0.6V. To limit the bias
current required for the external feedback resistor string
while maintaining good noise immunity, the minimum
suggested value for R2 is 59k. Although a larger value
will further reduce quiescent current, it will also increase
the impedance of the feedback node, making it more
sensitive to external noise and interference. Table 2
summarizes the resistor values for various output volt-
ages with R2 set to either 59k for good noise immu-
nity or 221k for reduced no load input current.
R3 =
V_OUT
V_REF
-1
· R4 =
1.5V
0.6V ^{- 1 · 59kΩ = 88.5kΩ}
The adjustable version of the AAT2148, combined with
an external feedforward capacitor (C3 in Figure 1),
delivers enhanced transient response for extreme pulsed
load applications. The addition of the feedforward capac-
itor typically requires a larger output capacitor C2 for
stability.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202009A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 28, 2012
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