AAT1147 Datasheet, PDF (9/18 Pages) Advanced Analogic Technologies – High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter

DATA SHEET
AAT1147
High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter
1
2
3
Enable
V_IN
C4
100pF
V_OUT =1.8V
R1
L1 ^118k
4.7μH
C1
10μF
C3
n/a
R2
59k
U1
AAT1147
1
8
EN PGND
2
7
OUT PGND
3
6
VIN PGND
4
5
LX AGND
C2
4.7μF
GND
GND2
LX
U1 AAT1147 SC70JW-8
L1 CDRH3D16-4R7
C2 4.7μF 10V 0805 X5R
C1 10μF 6.3V 0805 X5R
Figure 1: Enhanced Transient Response Schematic.
Control Loop
The AAT1147 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.
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
error amplifier reference is 0.6V.
Soft Start / Enable
Soft start limits the current surge seen at the input and
eliminates output voltage overshoot. When pulled low,
the enable input forces the AAT1147 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 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 VIN input.
Under-voltage lockout (UVLO) guarantees sufficient V_IN
bias and proper operation of all internal circuitry prior to
activation.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201986A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • May 23, 2012
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