AAT2500
1MHz Step-Down Converter/LDO Regulator
DATA SHEET
14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202014A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 4, 2012
Applications Information
Linear Regulator
Input and Output Capacitors
An input capacitor is not required for basic operation of
the linear regulator. However, if the AAT2500 is physically
located more than three centimeters from an input power
source, a CIN capacitor will be needed for stable operation.
Typically, a 1μF or larger capacitor is recommended for CIN
in most applications. CIN should be located as closely to
the device VIN pin as practically possible.
An input capacitor greater than 1μF will offer superior
input line transient response and maximize power supply
ripple rejection. Ceramic, tantalum, or aluminum elec-
trolytic capacitors may be selected for CIN. There is no
specific capacitor ESR requirement for CIN. However, for
300mA LDO regulator output operation, ceramic capaci-
tors are recommended for CIN due to their inherent capa-
bility over tantalum capacitors to withstand input current
surges from low impedance sources such as batteries in
portable devices.
For proper load voltage regulation and operational stabil-
ity, a capacitor is required between OUT and GND. The
COUT capacitor connection to the LDO regulator ground
pin should be made as directly as practically possible for
maximum device performance. Since the regulator has
been designed to function with very low ESR capacitors,
ceramic capacitors in the 1.0μF to 10μF range are rec-
ommended for best performance. Applications utilizing
the exceptionally low output noise and optimum power
supply ripple rejection should use 2.2μF or greater for
COUT
. In low output current applications, where output
load is less than 10mA, the minimum value for COUT can
be as low as 0.47μF.
Equivalent Series Resistance
ESR is a very important characteristic to consider when
selecting a capacitor. ESR is the internal series resistance
associated with a capacitor that includes lead resistance,
internal connections, size and area, material composi-
tion, and ambient temperature. Typically, capacitor ESR
is measured in milliohms for ceramic capacitors and can
range to more than several ohms for tantalum or alumi-
num electrolytic capacitors.
Bypass Capacitor and
Low Noise Applications
A bypass capacitor pin is provided to enhance the low
noise characteristics of the LDO. The bypass capacitor is
not necessary for operation; however, for best device
performance, a small ceramic capacitor in the range of
470pF to 10nF should be placed between the bypass pin
(BYP) and the device ground pin (GND). To practically
realize the highest power supply ripple rejection and low-
est output noise performance, it is critical that the capac-
itor connection between the BYP pin and GND pin be
direct and PCB traces should be as short as possible.
DC leakage on this pin can affect the LDO regulator out-
put noise and voltage regulation performance. For this
reason, the use of a low leakage, high quality ceramic
(NPO or C0G type) or film capacitor is highly recom-
mended.
L1
4.7μF
C1
VOUTBUCK
VIN
4.7μF
C4
10μF
C3
10nF
C5
VOUTLDO
PGND 1
LX 2
VP
3VCC 4
ENLDO
9
EN 10
FB 11
SGND 12
VLDO
5
OUT
6
GND
8
BYP
7
AAT2500
U1
L1
4.7μF
C1
VIN
R1
59k
R2
4.7μF
C4
10μF
C3
10nF
C5
VOUTLDO
VOUTBUCK
100pF
C8
PGND 1
LX 2
VP
3VCC 4
ENLDO
9
EN 10
FB 11
SGND 12
VLDO
5
OUT
6
GND
8
BYP
7
AAT2500
U1
Figure 1: AAT2500 Fixed Output. Figure 2: AAT2500 with Adjustable Step-Down
Output and Enhanced Transient Response.