AMS2263 datasheet(7/12 Pages) AMS

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OPERATION DESCRIPTION

The

AMS2263 is a highly integrated PWM

controller

optimized

for

offline

flyback

converter applications in sub 30W power range.

The extended burst mode control greatly reduces

the standby power consumption and helps the

design easily meet the international power

conservation requirements.

•

Startup Current and Start up Control

Startup current of

AMS2263 is designed to be very

low so that VDD could be charged up above

UVLO threshold level and device starts up quickly.

A large value startup resistor can therefore be

used to minimize the power loss yet provides

reliable startup in application.

For AC/DC

adaptor with universal input range design, a 2 MΩ,

1/8 W startup resistor could be used together with

a VDD capacitor to provide a fast startup and low

power dissipation solution.

•

Operating Current

The Operating current of

AMS2263 is low at 1.4mA.

Good efficiency is achieved with

AMS2263 low

operating current together with extended burst

mode control features.

•

Frequency shuffling for EMI improvement

The

frequency

Shuffling/jittering

(switching

frequency modulation) is

implemented in

AMS2263. The oscillation frequency is modulated

with a random source so that the tone energy is

spread out. The spread spectrum minimizes the

conduction band EMI and therefore reduces

system design challenge.

•

Extended Burst Mode Operation

At zero load or light load condition, majority of the

power dissipation in a switching mode power

supply is from switching loss on the MOSFET

transistor, the core loss of the transformer and the

loss on the snubber circuit. The magnitude of

power loss is in proportion to the number of

switching events within a fixed period of time.

Reducing switching events leads to the reduction

on the power loss and thus conserves the energy.

AMS2263 self adjusts the switching mode

according to the loading condition. At from no

load to light/medium load condition, the FB input

drops below burst mode threshold level. Device

enters Burst Mode control. The Gate drive output

switches only when VDD voltage drops below a

preset level and FB input is active to output an on

state. Otherwise the gate drive remains at off

state tominimize the switching loss and reduces

the standby power consumption to the greatest

extend. The frequency control also eliminates

the audio noise at any loading conditions.

•

Oscillator Operation

A resistor connected between RI and GND sets

the constant current source to charge/discharge

the internal cap and thus the PWM oscillator

frequency is determined.

The relationship

between RI and switching frequency follows the

below equation within the specified RI in Kohm

range at nominal loading operational condition.

•

Current Sensing and Leading Edge

Blanking

Cycle-by-Cycle current limiting is offered in

AMS2263 current mode PWM control. The switch

current is detected by a sense resistor into the

sense pin. An internal leading edge blanking

circuit chops off the sense voltage spike at initial

MOSFET on state due to Snubber diode reverse

recovery so that the external RC filtering on

AMS 2263

Advanced Monolithic Systems http://www.ams-semitech.com

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