AAT3110 Datasheet, PDF(11/18 Page) Advanced Analogic Technologies

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AAT3110 Datasheet, PDF (11/18 Pages) Advanced Analogic Technologies – MicroPower™ Regulated Charge Pump

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Functional Block Diagram

AAT3110

MicroPowerâ¢ Regulated Charge Pump

VIN

SHDN

CONTROL

VREF

C+

C-

VOUT

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 2ÃVIN 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-

3110.2001.9.0.92

GND

porarily placed in an idle state. When idle, the

AAT3110 has a quiescent current of 13ÂµA 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-

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 â CFLYÃ(2ÃVIN-VOUT)

The relative average current that the charge pump

can supply to the output may be approximated by

the following expression:

IOUT(AVG) Î± CFLYÃ(2ÃVIN-VOUT)ÃFSW

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 145Â°C. The charge

pump will remain disabled until the fault condition is

relieved.

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