AAT3110
MicroPower™ Regulated Charge Pump
Functional Block Diagram
VIN
S1
S3
S2
S4
SHDN
CONTROL
C+
C-
VREF
VOUT
-
+
GND
porarily placed in an idle state. When idle, the
AAT3110 has a quiescent current of 13µA or less.
The closed loop feed back 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 func-
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. On the second
phase, switches S1 and S4 are turned off (open), S2
and S3 are turned on (short). The low side of the fly-
ing 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
connected to output through a switch. For each
cycle phase, charge from input node VIN is trans-
ported 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
cycle stops and the charge pump circuit is tem-
tion 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 temper-
ature exceeds approximately 145°C. The charge
pump will remain disabled until the fault condition is
relieved.
3110.2001.9.0.92
11
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
