AAT2601 Datasheet, PDF (28/38 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

PRODUCT DATASHEET
AAT2601178
Total Power Solution for Portable Applications
Input/Output Capacitor and Inductor
Apart from the input capacitor that is shared with the LDO
inputs, only a small L-C filter is required at the output side
for the step-down converter to operate properly. Typically,
a 3.3μH inductor such as the Sumida CDRH2D11NP-
3R3NC and a 4.7μF ceramic output capacitor are recom-
mended for low output voltage ripple and small compo-
nent size. Ceramic capacitors with X5R or X7R dielectrics
are highly recommended because of their low ESR and
small temperature coefficients. A 10μF ceramic input
capacitor is sufficient for most applications.
Control Loop
The converter is a peak current mode step-down con-
verter. The inner, wide bandwidth loop controls the
inductor peak current. The inductor current is sensed
through the P-channel MOSFET (high side) which is also
used for short circuit and overload protection. A fixed
slope compensation signal is added to the sensed cur-
rent 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 inductor cur-
rent to force a constant output voltage for all load and
line conditions. The voltage feedback resistive divider is
internal and the error amplifier reference voltage is
0.45V. The voltage loop has a high DC gain making for
excellent DC load and line regulation. The internal volt-
age loop compensation is located at the output of the
transconductance voltage error amplifier.
Soft Start
Soft start slowly increases the internal reference voltage
when the input voltage or enable input is initially applied.
It limits the current surge seen at the input and elimi-
nates output voltage overshoot.
Current Limit and
Over-Temperature Protection
For overload conditions the peak input current is limited.
As load impedance decreases and the output voltage
falls closer to zero, more power is dissipated internally,
raising the device temperature. Thermal protection com-
pletely disables switching when internal dissipation
becomes excessive, protecting the device from damage.
The junction over-temperature threshold is 140°C with
15°C of hysteresis.
Linear LDO Regulators (OUT1-5)
The advanced circuit design of the linear regulators has
been specifically optimized for very fast start-up and
shutdown timing. These proprietary LDOs are tailored for
superior transient response characteristics. These traits
are particularly important for applications which require
fast power supply timing.
There are two LDO input pins, AVIN1/2, which should be
connected to the SYSOUT LDO output pin. All LDO outputs
are initially fixed at 3.0V. The user can program the output
voltages for the LDOs to 2.8V, 2.85V, or 2.9V using I²C.
The high-speed turn-on capability is enabled through the
implementation of a fast start control circuit, which
accelerates the power up behavior of fundamental con-
trol and feedback circuits within the LDO regulator. For
LDO4 and LDO5, fast turn-off time response is achieved
by an active output pull down circuit, which is enabled
when the LDO regulator is placed in the shutdown mode.
This active fast shutdown circuit has no adverse effect on
normal device operation.
Input/Output Capacitors
The LDO regulator output has been specifically optimized
to function with low cost, low ESR ceramic capacitors.
However, the design will allow for operation over a wide
range of capacitor types. The input capacitor is shared
with all LDO inputs and the step-down converter. A 10μF
is sufficient. A 4.7μF ceramic output capacitor is recom-
mended for LDO2-5 and a 22μF output capacitor for
LDO1.
Current Limit and
Over-Temperature Protection
The regulator comes with complete short circuit and
thermal protection. The combination of these two internal
protection circuits gives a comprehensive safety system
to guard against extreme adverse operating conditions.
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2601.2008.01.1.0