AAT2782_12 Datasheet, PDF (14/22 Pages) Skyworks Solutions Inc. – Triple-Output PMIC Dual Buck with Low-VIN LDO

DATA SHEET
AAT2782
Triple-Output PMIC: Dual Buck with Low-V_IN LDO
Functional Description
The AAT2782 is a 3-channel high performance power
management IC. Channel 1 is a 1200mA step-down con-
verter. Channel 2 is a 600mA step-down converter.
Channel 3 is a 400mA LDO regulator with low-input volt-
age capability and low output noise for sensitive analog
applications.
The low input voltage capability of the LDO regulator
allows the step-down converter to be tied directly to the
LDO input. This configuration provides the efficiency
benefits of a switching converter plus the low noise ben-
efits of a LDO (low drop-out) regulator.
Channel 1 and 2: 1200/600mA
Step-Down (Buck) Converters
The AAT2782 Channel 1 and 2 step-down converters are
peak current mode PWM converters operating at 1.3MHz
frequency. The input voltage range is 2.7V to 5.5V. The
output voltage range is 0.6V to V_IN and is adjustable with
an external resistor divider. The converters provide
internal compensation. Power devices are sized for 1A
output current while maintaining over 85% efficiency at
full load. Peak efficiency is above 95%. Light load effi-
ciency is maintained at greater than 80% down to 85%
of full load current. Channel 2 has excellent transient
response and load and line regulation. Transient response
time is typically less than 20μs.
The enable inputs, when pulled low, force the converter
into a low power non-switching state consuming less
than 1μA of current.
For overload conditions, the peak input current is limit-
ed. Also, thermal protection completely disables switch-
ing if internal dissipation becomes excessive, thus pro-
tecting the device from damage. The junction over-
temperature threshold is 130°C with 20°C of hysteresis.
Under-voltage lockout (UVLO) guarantees sufficient V_IN
bias and proper operation of all internal circuits prior to
activation.
Control Loop
The AAT2782 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 cur-
rent mode loop for the necessary peak switch current to
force a constant output voltage for all load and line con-
ditions. 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. When pulled low,
the enable input forces the AAT2782 into a low-power,
non-switching state. The total input current during shut-
down is less than 1μA.
Low Dropout Operation
For conditions where the input voltage drops to the out-
put voltage level, the converter duty cycle increases to
100%. As the converter approaches the 100% duty
cycle, the minimum off-time initially forces the high side
on-time to exceed the 1.3MHz clock cycle and reduces
the effective switching frequency. Once the input drops
below the level where the converter can regulate the
output, the high side P-channel MOSFET is enabled con-
tinuously 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.
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 protec-
tion completely disables switching when internal dissipa-
tion becomes excessive. The junction over-temperature
threshold is 130°C with 20°C of hysteresis. Once an
over-temperature or over-current fault conditions is
removed, the output voltage automatically recovers.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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202038A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 8, 2012