PRODUCT DATASHEET
AAT2610
7-Channel PMU for Digital Still Cameras
drop across the parasitical body diode. If true load dis-
connection is required, an external PMOSFET controlled
by SEQ can be adopted.
Light Load Mode and
Normal PWM Control
The AAT2610 uses light load mode to enhance the effi-
ciency at light load. In light load mode, if the error
amplifier output signal is lower than a given level at a
certain clock point, the switch pulse is skipped to reduce
dominant switching losses.
Synchronous Step-Down
DC to DC Converter
The AAT2610 has two synchronous step-down DC-DC
converters. Their output voltages can be programmed
from 0.6V to VIN by an external resistor divider.
In normal PWM mode to the buck converter, the current
through the P-channel (high side) is sensed for current
loop control. The P-channel current limit is used to pre-
vent internal power PMOSFET overstress or damage by
the high power. To the boost converter, the current though
the N-channel (low side) is sensed for the control loop and
its current limit also protects the main MOSFET.
At dropout, the converter’s duty cycle equals 100% and
the output voltage tracks the input voltage minus the
voltage drop across the P-channel MOSFET. At low input
supply voltage, the RDS(ON) of the P-channel MOSFET
increases, and the efficiency of the converter decreases.
The 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. The inter-
nal fixed slope compensation is employed to eliminate
the sub-harmonic oscillation and keep regulation stable
when the duty cycle is over 50%.
The two step-down converters adopt soft-start to elimi-
nate output voltage overshoot when the enable or input
voltage is applied. When the ENSD1 and ENSD2 are
pulled low, the outputs of the two SD converters are
down to zero and its shutdown current is below 1μA.
Non-Synchronous Step-Up and Buck/
Boost (Inverting) DC to DC Converters
Fault Protection
Two non-synchronous step-up converters are targeted
for LCD backlight and CCD positive loads. The controllers
regulate the output voltage by modulating the pulse
width of the internal NMOSFET. External schottky diode
and power inductor are required to set up the boost. The
output voltage can be programmed from 5V to 20V by
external divider.
Short-Circuit and Overload Protection
When any of the converters’ output voltage is lower than
the programmed value for a certain period of time
(100,000 clock cycles, typically 66.7ms), the central
control circuits treat it as an overload situation; all seven
channels will be turned off and SCF will be pulled low
until the IC is restarted either by SU enable pin (ENSU)
reset or re-application of the input voltage. During over-
load period, the peak current limit prevents the main
switch (NMOSFET of step-up converter and PMOSFET of
step-down converter) from overstress and damage, and
also avoids saturation of the external inductor. For syn-
chronous step-up (SU) channels, overload protection
function is disabled in “bypass” mode.
Auxiliary 1 is ideally designed for driving typical 4 serial
white LEDs. The maximum current flowing through the
WLED string is sensed at CSL1 and set to 20mA by the
internal ballast resistor with ±10% accuracy. The industry
standard PWM (Pulse Width Modulation) controlling tech-
nology is adopted to program the WLED current. Applying
a 10% ~100% duty cycle PWM signal with the frequency
range 1kHz to 30kHz at ENL1 can get 2mA to 20mA
WLED current. If an open circuit occurs, the internal
over-voltage protection circuit prevents damage to the
converter within 67ms, then shuts down all channels.
Over-Temperature Protection
Thermal protection completely disables power MOSFET
switching when internal power dissipation becomes
excessive. Only reference and internal clock are still
active in this condition. Once the over-temperature con-
dition is removed, the output voltages automatically
recover. The junction over-temperature threshold is
140°C with 15°C of hysteresis.
Auxiliary 2 is designed for +15V CCD bias. Soft-start is
adopted to eliminate the output voltage overshoot and
decrease the effect on the input voltage.
Auxiliary 3 is non-synchronous buck-boost (inverting)
DC to DC converter which is targeted for negative CCD
loads with low noise. Soft-start is adopted to limit the
inrush current at startup.
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