AIC1639 데이터 시트보기 (PDF) - Analog Intergrations

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AIC1639

3-PIN ONE-CELL STEP-UP DC/DC CONVERTER

Analog Intergrations 

AIC1639

3-PIN ONE-CELL STEP-UP DC/DC CONVERTER

SPEC NO: DS-1639-00 05/26/00

■ APPLICATION INFORMATION

GENERAL DESCRIPTION

AIC1639 PFM (pluse frequency modulation) controller

ICs combine a switch mode regulator, push pull driver

(AIC1639), precision voltage reference, and voltage

detector in a single monolithic device. They offer both

extreme low quescient current, high efficiency, and

very low gate threshold voltage to ensure start-up with

low battery voltage ( 0.8V typ.). Designed to maxi-

mize battery life in protable products, and minimize

switching losses by only switching as needed service

the load.

PFM controllers transfer a discreate amount of energy

per cycle and regulate the output voltage by modulat-

ing switching frequency with the constant turn-on time.

Switching frequency depends on load, input voltage,

and inductor value, and it can range up to 100KHz.

mode. Continuous conduction mode means that the

inductor current does not ramp to zero during each

cycle.

VIN

IIN

SW

EXT

Isw

ID

IOUT

+

VOUT

Ico

VEXT

IIN

I PK

When the output voltage drops, the error comparator

enable 100kHz oscillator that turns on the MOSFET

around 7.5us and 2.5us off time. Turning on the

MOSFET allows inductor current to ramp up, storing

energy in a magnetic field. When MOSFET turns off

that forces inductor current through diode to the out-

put capacitor and load. As the stored energy is de-

pleted, the current ramp down until the diode turns off.

At this point, inductor may ring due to residual energy

and stray capacitance. The output capacitor stores

charge when current flowing through the diode is high,

and release it when current is low, thereby maintain-

ing a steady voltage across the load.

ISW

Charge Co.

ID

IOUT

TDIS Discharge Co.

VSW

t

Discontinuous Conduction Mode

As the load increases, the output capacitor dis-

charges faster and the error comparator initiates cy-

cles sooner, increasing the switching frequency. The

maximum duty cycle ensure adequate time for energy

tranfer to output during the second half each cycle.

Depending on circuit, PFM controller can operate in

either discontinuous mode or continuous conduction

ANALOG INTEGRATIONS CORPORATION

www.analog.com.tw

4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510

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