AAT1153 Datasheet, PDF (11/19 Pages) Advanced Analogic Technologies – 2A Step-Down Converter

Applications Information
VIN 2.5V-5.5V
C1
22μF
1
EN
LX ⁸
2 _IN
LX ⁷
3 _{AIN AAT1153-0.6 FB} 5
6 _AGND
4 _AGND
PGND ¹⁰
PGND ⁹
L1
2.2μH
C3
22pF
VOUT
1.8V, 2A
R1
634kΩ ^C2
22μF
R2
316kΩ
Figure 1: Basic Application Circuit.
Setting the Output Voltage
Figure 1 shows the basic application circuit for the
AAT1153. The AAT1153 can be externally programmed.
Resistors R1 and R2 in Figure 1 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 1
summarizes the resistor values for various output volt-
ages with R2 set to either 59k for good noise immunity
or 316k for reduced no load input current.
The AAT1153, combined with an external feed forward
capacitor (C3 in Figure 1), delivers enhanced transient
response for extreme pulsed load applications. The addi-
tion of the feed forward capacitor typically requires a
larger output capacitor C2 for stability. The external
resistor sets the output voltage according to the follow-
ing equation:
V_OUT = 0.6V ·
⎛⎝_{1 +}
R1 ⎞
R2 ⎠
R1 =
⎛
⎝
V_OUT
0.6V
-
1 ^⎞⎠
· R2
Table 1 shows the resistor selection for different output
voltage settings.
DATA SHEET
AAT1153
2A Step-Down Converter
V_OUT (V)
0.8
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 = 59k
R1 (k)
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
R2 = 316k
R1 (k)
105
158
210
261
316
365
422
475
634
655
732
1000
1430
Table 1: Resistor Selections for Different Output
Voltage Settings (Standard 1% Resistors
Substituted For Calculated Values).
Inductor Selection
For most designs, the AAT1153 operates with inductor
values of 1μH to 4.7μH. Low inductance values are
physically smaller but require faster switching, which
results in some efficiency loss. The inductor value can
be derived from the following equation:
L = ^{VOUT · (VIN - VOUT)}
V_IN · ΔI_L · f_OSC
Where I_L is inductor ripple current. Large value induc-
tors lower ripple current and small value inductors result
in high ripple currents. Choose inductor ripple current
approximately 30% of the maximum load current 2A, or
ΔI_L = 600mA
For output voltages above 2.0V, when light-load effi-
ciency is important, the minimum recommended induc-
tor is 2.2μH.
Manufacturer’s specifications list both the inductor DC
current rating, which is a thermal limitation, and the
peak current rating, which is determined by the satura-
tion characteristics. The inductor should not show any
appreciable saturation under normal load conditions.
Some inductors may meet the peak and average current
ratings yet result in excessive losses due to a high DCR.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201992B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
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