AAT2113B Datasheet, PDF (12/22 Pages) Skyworks Solutions Inc. – 3.3MHz, Fast Transient 1.5A Step-Down Converter in an 2mm x 2mm Package

DATA SHEET
AAT2113B
3.3MHz, Fast Transient 1.5A Step-Down Converter in an 2mm x 2mm Package
Control Loop
The AAT2113B is a peak current mode step-down con-
verter. The current through the P-channel MOSFET (high
side) is sensed for current loop control, as well as short-
circuit and overload protection. A fixed slope compensa-
tion signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak
current mode loop appears as a voltage-programmed
current source in parallel with the output capacitor.
The output of the voltage error amplifier programs the
current mode loop for the necessary peak switch current
to force a constant output voltage for all load and line
conditions. Internal loop compensation terminates the
transconductance voltage error amplifier output. The
reference voltage is internally set to program the con-
verter output voltage greater than or equal to 0.6V.
Soft Start/Enable
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. The enable input,
when pulled low, forces the AAT2113B into a low-power,
non-switching state. The total input current during shut-
down is less than 1μA.
Current Limit and
Over-Temperature Protection
For overload conditions, the peak input current is limit-
ed. To minimize power dissipation and stresses under
current limit and short-circuit conditions, switching is
terminated after entering current limit for a series of
pulses. Switching is terminated for seven consecutive
clock cycles after a current limit has been sensed for a
series of four consecutive clock cycles.
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 140°C with 25°C of hys-
teresis. Once an over-temperature or over-current fault
condition 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.
For applications where the duty cycle is less than 50%,
the inductor values can be chosen freely.
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.
For low cost application and a sufficiently small footprint
in a 5x5mm area, the LQM2HPNR47MG0 shielded chip
inductor, which has 40mΩ DCR and 1.8A DC current rat-
ing, is selected for 1.2V output.
The inductors listed in Table 1 have been used with the
AAT2113B.
Manufacturer
Murata
Coilcraft
Part Number
LQM2HPNR47MG0
EPL2010-421ML
EPL2010-681ML
Value (μH)
0.47 ± 20%
0.42 ± 20%
0.68 ± 20%
DC Resistance (Ω)
0.04 ± 25%
0.04 ± 25%
0.058 ± 25%
Table 1: AAT2113B List of Inductors.
Size (mm)
2.5x2.0x1.0
2.0x2.0x1.0
2.0x2.0x1.0
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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202003A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 24, 2012