AAT2510 Datasheet, PDF (9/19 Pages) Advanced Analogic Technologies – Dual 400mA, 1MHz Step-Down DC-DC Converter

DATA SHEET
AAT2510
Dual 400mA, 1MHz Step-Down DC/DC Converter
V_IN = 2.7 - 5.5V
C3
10μF
2.5V at 400mA _L1
4.7μH
C1
4.7μF
U1
AAT2510
12
VIN1
9
VIN2
1
EN1
4
EN2
11
LX1
8
LX2
2
FB1
5
FB2
3
6
SGND1 SGND2
10
GND1
7
GND2
C8
0.1μF
1.8V at 400mA
L2
4.7μH
C2
4.7μF
L1, L2 Sumida CDRH3D16-4R7 C1, C2 Murata GRM219R61A475KE19
C3 Murata GRM21BR60J106KE19
Figure 1: AAT2510 Fixed Output.
VIN
C3
10μF
1.8V
C4
100pF
L1
4.7μH
C1
10μF
R1
118k
R2
59.0k
U1
AAT2510
12
VIN1
9
VIN2
1
EN1
4
EN2
11
LX1
8
LX2
2
FB1
5
FB2
3
6
SGND1 SGND2
10
GND1
7
GND2
C8
0.1μF
2.5V
L2
10μH
C5
100pF
R4
59.0k
R3
187k
C2
10μF
Figure 2: AAT2510 Adjustable Output with
Enhanced Transient Response.
Low Dropout Operation
For conditions where the input voltage drops to the out-
put voltage level, the converter duty cycle increases to
100%. As 100% duty cycle is approached, the minimum
off-time initially forces the high side on-time to exceed
the 1MHz clock cycle and reduce the effective switching
frequency. Once the input drops below the level where
the output can be regulated, the high side P-channel
MOSFET is turned on continuously for 100% duty cycle.
At 100% duty cycle, the output voltage tracks the input
voltage minus the I*R drop of the high side P-channel
MOSFET R_DS(ON).
Low Supply
The under-voltage lockout (UVLO) feature guarantees
sufficient V_IN bias and proper operation of all internal
circuitry prior to activation.
Fault Protection
For overload conditions, the peak inductor current is lim-
ited. Thermal protection disables switching when the
internal dissipation or ambient temperature becomes
excessive. The junction over-temperature threshold is
140°C with 15°C of hysteresis.
Applications Information
Inductor Selection
The step-down converter uses peak current mode con-
trol with slope compensation to maintain stability for
duty cycles greater than 50%. The output inductor value
must be selected so the inductor current down slope
meets the internal slope compensation requirements.
The internal slope compensation for the adjustable and
low-voltage fixed versions of the AAT2510 is 0.24A/μsec.
This equates to a slope compensation that is 75% of the
inductor current down slope for a 1.5V output and 4.7μH
inductor.
m
=
0.75 ⋅
L
V_O
=
0.75 ⋅ 1.5V
4.7μH
=
0.24
A
μsec
This is the internal slope compensation for the adjust-
able (0.6V) version or low-voltage fixed version. When
externally programming the 0.6V version to a 2.5V out-
put, the calculated inductance would be 7.5μH.
L=
0.75 ⋅ V_O
m
=
0.75V
0.24A /μsec
≈
3
μsec
A
⋅ V_O
μsec
= 3 _A ⋅ 2.5V = 7.5μH
In this case, a standard 10μH value is selected. For
high-voltage fixed versions (2.5V and above), m =
0.48A/μsec. Table 1 displays inductor values for the
AAT2510 fixed and adjustable options.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202020B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 19, 2013
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