AAT3110
MicroPower™ Regulated Charge Pump
Functional Block Diagram
VIN
S1
S3
S2
S4
SHDN
CONTROL
C+
C-
VREF
VOUT
-
+
GND
cycle stops and the charge pump circuit is tem-
porarily placed in an idle state. When idle, the
AAT3110 has a quiescent current of 13µA or less.
The closed loop feedback system containing the
voltage sense circuit and control comparator allows
the AAT3110 to provide a regulated output voltage to
the limits of the input voltage and output load cur-
rent. The switching signal, which drives the charge
pump, is created by an integrated oscillator within
the control circuit block. The free-running charge
pump switching frequency is approximately 750kHz.
The switching frequency under an active load is a
Functional Description
Operation (Refer to block diagram)
The AAT3110 uses a switched capacitor charge
pump to boost an input voltage to a regulated output
voltage. Regulation is achieved by sensing the
charge pump output voltage through an internal
resistor divider network. A switched doubling circuit
is enabled when the divided output drops below a
preset trip point controlled by an internal comparator.
The charge pump switch cycling enables four inter-
nal switches at two non-overlapping phases. During
the first phase, switches S1 and S4 are switched on
(short) and switches S2 and S3 are off (open). The
flying capacitor CFLY is charged to a level approxi-
mately equal to input voltage VIN. During the second
phase, switches S1 and S4 are turned off (open) and
switches S2 and S3 are turned on (short). The low
side of the flying capacitor CFLY is connected to GND
during the first phase. During the second phase, the
flying capacitor CFLY is switched so that the low side
is connected to VIN. The voltage at the high side of
the flying capacitor CFLY is bootstrapped to 2 × VIN
and is connected to output through a switch. For
each cycle phase, charge from input node VIN is
transported from a lower voltage to a higher voltage.
This cycle repeats itself until the output node voltage
is high enough to exceed the preset input threshold
of the control comparator. When the output voltage
exceeds the internal trip point level, the switching
function of VIN, VOUT, COUT, and IOUT
.
For each phase of the switching cycle, the charge
transported from VIN to VOUT can be approximated
by the following formula:
VPHASE ≈ CFLY × (2 × VIN - VOUT
)
The relative average current that the charge pump
can supply to the output may be approximated by
the following expression:
IOUT(AVG) α CFLY × (2 × VIN - VOUT) × FSW
The AAT3110 has complete output short-circuit and
thermal protection to safeguard the device under
extreme operating conditions. An internal thermal
protection circuit senses die temperature and will shut
down the device if the internal junction temperature
exceeds approximately 145°C. The charge pump will
remain disabled until the fault condition is relieved.
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3110.2005.11.1.4
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
