AAT2603_08 Datasheet, PDF (20/26 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

PRODUCT DATASHEET
AAT2603
Total Power Solution for Portable Applications
R1 =
V_OUT
V_REF
-1
· R2 =
1.5V
0.6V ^{- 1 · 59kΩ = 88.5kΩ}
The AAT2603 step-down regulators, combined with an
external feedforward capacitor (C_FF in Figure 1), deliver
enhanced transient response for extreme pulsed load
applications.
C_FF
VFBB1/VFBB2
VDC-DC1/VDC-DC2
R1
R2
Figure 1: AAT2603 DC-DC1/DC-DC2 External
Resistor Output Voltage Programming.
V_OUT (V)
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
R2 = 59kΩ
R1 (kΩ)
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
R2 = 221kΩ
R1 (kΩ)
113K
150K
187K
221K
261K
301K
332K
442K
464K
523K
715K
1.00M
Table 4: Feedback Resistors
for DC-DC1 and DC-DC2.
LDO1/LDO2/LDO3/LDO4
Input Capacitor
Typically, a 2.2μF or larger capacitor is recommended for
C_INL12/C_INL34/C_AIN in most applications. The input capacitor
should be located as close to the input (INL12/INL34/
AIN) of the device as practically possible. C_INL12/C_INL34/
C_AIN values greater than 2.2μF will offer superior input
line transient response and will assist in maximizing the
highest possible power supply ripple rejection.
Ceramic, tantalum, or aluminum electrolytic capacitors
may be selected for C_INL12/C_INL34/C_AIN. There is no specific
capacitor ESR requirement for C_INL12/C_INL34/C_AIN. However,
for 200mA/400mA LDO regulators output operation,
ceramic capacitors are recommended for C_INL12/C_INL34/C_AIN
due to their inherent capability over tantalum capacitors
to withstand input current surges from low impedance
sources such as batteries in portable devices.
Output Capacitor
For proper load voltage regulation and operational stabil-
ity, a capacitor is required between pins VOUTLX and
AGND. The C_OUTLX capacitor connection to the LDO regu-
lator ground pin should be made as direct as practically
possible for maximum device performance.
The AAT2603 LDO regulators have been specifically
designed to function with very low ESR ceramic capaci-
tors. Although the device is intended to operate with
these low ESR capacitors, it is stable over a very wide
range of capacitor ESR, thus it will also work with higher
ESR tantalum or aluminum electrolytic capacitors.
However, for best performance, ceramic capacitors are
recommended.
Typical output capacitor values for maximum output cur-
rent conditions range from 4.7μF to 10μF. If desired,
C_OUTLX may be increased without limit.
Bypass Capacitor and Low Noise Applications
A bypass capacitor pin is provided to enhance the very
low noise characteristics of the AAT2603 LDO3 and LDO4
regulators. The bypass capacitor is not necessary for
operation of the AAT2603. However, for best device per-
formance, a small ceramic capacitor should be placed
between the bypass pin (BYP) and the device analog
ground pin (AGND). The value of C_BYP should be 10nF. For
lowest noise and best possible power supply ripple rejec-
tion performance a 10nF capacitor should be used. To
practically realize the highest power supply ripple rejec-
tion and lowest output noise performance, it is critical
that the capacitor connection between the BYP pin and
AGND pin be direct and PCB traces should be as short as
possible. Refer to the PCB Layout Recommendations sec-
tion of this datasheet for examples.
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2603.2008.10.1.2