PRODUCT DATASHEET
AAT2610
7-Channel PMU for Digital Still Cameras
Start-Up
Functional Description
The AAT2610's major control circuitries adopt power
from the SU converter output and do not function at less
than 2.7V. To ensure the PMIC can start up at VIN as low
as 1.8V, the step-up converter employs a startup oscilla-
tor with a typical 200kHz frequency. The startup oscilla-
tor drives the internal N-channel MOSFET at LXSU until
the SU converter output voltage reaches 2.7V, at which
point the current-mode PWM circuitry takes over. A
startup current limit (750mA) and NMOSFET off time
(700ns) decrease the startup inrush current. At low input
voltages, the AAT2610 may have difficulty starting up
with heavy loads.
The AAT2610 PMIC is targeted for single cell Li-ion bat-
tery or dual cell Alkaline battery applications. It includes
seven integrated step-up and step-down converters,
including one synchronous step-up converter (SU), two
synchronous step-down converters (SD1, SD2), one
synchronous step-up or step-down converter (Main), two
non-synchronous step-up converters (AUX1, AUX2) and
one non-synchronous buck-boost (inverting) converter
(AUX3).
The SU converter is the key channel. Its output powers
all internal control and reference circuits when the out-
put voltage is above 2.7V. The AUX1 converter is spe-
cially designed for 1 to 6 white LED serial backlight
applications. Its current sink pin (CSL1) is suitable to
control WLED current to up to 20mA. AUX3 is a transfor-
merless inverting converter which controls the internal
P-channel MOSFET to regulate negative voltage.
Under-Voltage Lockout
Independent UVLO (Under-Voltage Lockout) circuitry
guarantees the sufficient input power and proper opera-
tion of all internal circuitry. When input voltage at VIN
rises above 1.8V, the AAT2610 leaves UVLO status and
enters the startup process. Once in regulation, the VIN
power can be as low as 1.6V before the AAT2610 enters
UVLO status.
The AAT2610 uses a fixed-frequency peak current control
architecture. Light load mode is used to enhance light
load efficiency. Compensation is integrated to reduce the
number of external components and achieve excellent
transient response and load and line regulation.
Bypass Mode
When the SU converter input voltage increases above the
bypass mode threshold (typically 4.75V), the step-up
converter enters “bypass” mode, which automatically
connects the input to the output. In this mode, P-channel
synchronous MOSFET is always ON and N-channel
MOSFET is always off. The output voltage follows input
voltage in the mode and overload protection is disabled.
The ideal 1.5MHz switching frequency allows the use of
smaller output filter components for improved power
density, reduced external component size, and optimized
output voltage ripple. The output voltages can be pro-
grammed by an external divider.
The AAT2610 has seven separate enable pins to control
each converter's startup. A 1.4ms startup delay is
employed to guarantee that the key SU converter is
already in regulation and the internal control and the
reference have been normally biased before the other six
converters start up.
Synchronous Step-Up /
Step-Down DC to DC Converter
The AAT2610 has one synchronous step-up/step-down
DC-DC converter which is ideally designed for 2AA/Li-ion
applications. The SUSD pin is used to set the operation
mode. When SUSD is set to logic high, the step-up con-
verter setting is selected. N-channel switch transistor
current is sensed for current loop control to regulate the
output over the complete load range; when SUSD is
pulled low, the step-down converter type is set and the
P-channel switch transistor current is sampled for the
current control loop. In both converter types, soft-start
is employed to suppress the startup inrush current and
eliminate the output voltage overshoot.
Synchronous Step-Up DC to DC Converter
The AAT2610 has one synchronous step-up DC-DC con-
verter. It utilizes internal power MOSFETs to achieve high
efficiency over the full load current range. The external
feedback can program the output voltage between 3.0V
to 5.5V. Its “bypass” mode automatically connects the
input to the output when the input voltage is higher than
the bypass mode threshold. In shutdown, the enable pin
(ENSU) is pulled low, the SU converter output is equal to
the input voltage minus a voltage drop across the para-
sitical body diode, and all other channels are shut down
regardless of their enable setting.
In shutdown with the enable pin (ENM) pulled low, if the
step-down converter is selected, the converter is forced
into a non-switching state and the output voltage drops
to zero. When the step-up converter is selected, the out-
put voltage is equal to the input voltage minus a voltage
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