PRODUCT DATASHEET
AAT2113A
TM
SwitchReg
3MHz, FastTransient 1.5A Step-Down Converter in 2mm x 2mm Package
teresis. Once an over-temperature or over-current fault
condition is removed, the output voltage automatically
recovers.
Control Loop
The AAT2113A 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 cur-
rent mode loop appears as a voltage-programmed cur-
rent source in parallel with the output capacitor.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VCC
input. Under-voltage lockout (UVLO) guarantees suffi-
cient VIN bias and proper operation of all internal cir-
cuitry prior to activation.
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.
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.
Soft Start/Enable
For applications where the duty cycle is less than 50%,
the inductor values can be chosen freely.
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. The enable input,
when pulled low, forces the AAT2113A into a low-power,
non-switching state. The total input current during shut-
down is less than 1ꢀA.
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.
Current Limit and
Over-Temperature Protection
Some inductors may meet the peak and average current
ratings yet result in excessive losses due to a high DCR.
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.
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.
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 140°C with 15°C of hys-
The inductors listed in Table 1 have been used with the
AAT2113A.
Manufacturer
Part Number
Value (μH)
DC Resistance (Ω)
Size (mm)
Murata
LQM2HPNR47MG0
EPL2010-421ML
EPL2010-681ML
0.47 ± 20%
0.42 ± 20%
0.68 ± 20%
0.04 ± 25%
0.04 ± 25%
0.058 ± 25%
2.5x2.0x1.0
2.0x2.0x1.0
2.0x2.0x1.0
Coilcraft
Table 1: AAT2113A List of Inductors.
w w w . a n a l o g i c t e c h . c o m
10
2113A.2009.06.1.1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
