AAT2114A Datasheet, PDF (11/16 Pages) Skyworks Solutions Inc. – 2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator

DATA SHEET
AAT2114A
2.5A Low-Noise, Fast Transient 3MHz Step-Down Regulator
Current Limit and
Over-Temperature Protection
For overload conditions, the peak input current is limit-
ed. The on-time is terminated after a current limit has
been sensed.
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 140°C with 15°C of hys-
teresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VCC
input. Under-voltage lockout (UVLO) guarantees suffi-
cient V_IN bias and proper operation of all internal cir-
cuitry prior to activation.
Component Selection
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 inductor value can be calculated by:
L1 = ^{0.47 · VOUT}
1.2
For low cost application and a sufficiently small footprint,
the TDK VLS252012T-R47N2R1 shielded chip inductor,
which has 47mΩ DCR, is selected for 1.2V output (see
Table 1).
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.
Always consider the losses associated with the DCR and
its effect on the total converter efficiency when selecting
an inductor.
Input Capacitor
Select a 10μF to 22μF X7R or X5R ceramic capacitor for
the input. To estimate the required input capacitor size,
determine the acceptable input ripple level (V_PP) and solve
for C_IN. The calculated value varies with input voltage and
is a maximum when V_IN is double the output voltage.
C_IN(MIN) =
D · (1 - D)
V_PP
I_O
- ESR
· F_SW
D=
V_O
V_IN
The peak ripple voltage occurs when V_IN = 2x V_O (50%
duty cycle), resulting in a minimum output capacitance
recommendation:
C_IN(MIN) =
1
V_PP
I_O
- ESR
· 4 · F_S
Always examine the ceramic capacitor DC voltage coef-
ficient characteristics when selecting the proper value.
For example, the capacitance of a 10μF, 6.3V, X5R
ceramic capacitor with 5.0V DC applied is actually about
6μF. The maximum input capacitor RMS current is:
I_RMS = I_O · D · (1 - D)
I_RMS = I_O ·
V_{O · 1 -} V_O
V_IN
V_IN
V_OUT (V)
1.2
1.8
2.5
3.3
Inductor Selection
TDK, VLS252012T-R47N2R1, 0.47μH, I_SAT = 3.7A, DCR = 47mΩ
Sumida, CDRH38D16R/HP, 0.9μH, I_SAT = 2.66A, DCR = 20mΩ
TDK, VLS252012T-1R0N1R7, 1.0μH, I_SAT = 2.7A, DCR = 88mΩ
TDK, VLF5014AT-1R5M1R7, 1.5μH, I_SAT = 2.9, DCR = 51mΩ
Table 1: Inductor Selection.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202004C • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 18, 2013
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