WS2273 datasheet(7/9 Pages) WINSEMI

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WS2273

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Function

Function Description

Description

2273 is a high performance current mode PWM

controller, optimized for low power AC/DC application.

Ultra low startup current and operating current together

with burst mode feature minimize the standby power

consumption and improve the switching efficiency. In

addition to reduce the external component count, the

internal synchronous slope compensation combines with

the

leading-edge blanking

improves

system

large

stability

and

reduces

the

possible

subharmonic

oscillation. 2273 also have multiform general recovery

protection mode. The main function is described as

below .

Startup

Startup Current

Current

Current and

and

and Startup

Startup

Startup Control

Control

Startup current of 2273 is designed to be extremely low

at 5uA, so that VCC 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, predigest the design of startup circuit and

provides reliable startup in application. For the design of

AC/DC adaptor with universal input range, a startup

resistor of 2 M Ω , 1/8 W could be used together with a

VCC capacitor to provide a fast startup and low power

dissipation solution.

Operating

Operating Current

Current

The operating current of 2273 is low at 1.8mA. Excellent

efficiency is achieved with low operating current together

and extended burst mode control circuit.

Soft

Soft Start

Start

2273 features an internal 4ms soft start to soften the

electrical stress occurring in the power supply during

startup. It is activated during the power on sequence. As

soon as VCC reaches UVLO （ OFF ）， the CS peak

voltage is gradually increaced from 0.15V to the

maximum level. Every restart up is followed by a soft

start.

Extended

Extended Burst

Burst

Burst Mode

Mode

Mode Operation

Operation

At zero load or light load, most of the power dissipation

of the switching power supply comes from the MOSFET

switching loss, 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 period of time. Therefore reducing the switch event

leads to reduction on the power loss and thus saving the

energy.

For the burst mode control circuit, 2273 self adjusts the

switching mode according to the loading condition. At the

condition of no load or light/medium load, the FB input

voltage drops below burst mode threshold level. Device

enters Burst Mode control on the basis of the judgment.

The gate drive output switches only when VCC voltage

drops below a preset level and FB input is active.

Otherwise the gate drive remains at off to minimize the

switching loss and power consumption to the greatest

extend. The frequency control also eliminates the audio

noise at any loading conditions.

Oscillator

Oscillator Operation

Operation

The switching frequency is internally fixed at 65kHz. No

external frequency setting components are required for

PCB design simplification.

Current

Current Sensing

Sensing

Sensing and

and

and Leading

Leading

Leading Edge

Edge

Edge Blanking

Blanking

Cycle-by-Cycle current limiting is offered in 2273. 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 sense input is no longer required.

The current limit comparator is disabled and thus cannot

turn off the internal MOSFET during the blanking period.

PWM duty cycle is determined by the current sense input

voltage and the FB input voltage.

Internal

Internal Synchronized

Synchronized

Synchronized Slope

Slope

Slope Compensation

Compensation

Built-in slope compensation circuit adds slope voltage

onto the current sense input voltage for PWM generation.

This greatly enhances the close loop stability at CCM

and prevents possible subharmonic oscillation and thus

reduces the output ripple voltage.

Gate

Gate Drive

Drive

The gate drive strength which is too weak leads to over

switch loss of MOSFET while too strong gate drive

output compromises in the over EMI. A good tradeoff

between output strength and dead time control is

achieved through the design of the built-in totem pole

gate. The low standby dissipation and good EMI system

WS2273 Datasheet(PDF) 7 Page - Shenzhen Winsemi Microelectronics Co., Ltd

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