WS2259DP datasheet(7/11 Pages) WINSEMI

7 / 11 page

Rev.A Apr.2011

WS2259

Steady,

Steady, keep

keep

keep you

you

you advance

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Function

Function Description

Description

WS2259 is a highly integrated current mode PWM control

IC which is optimized for high performance. It is applied

for switch power of the small-sized and medium-sized for

example the power adaptor. The low startup current,

operation current and burst mode function at the condition

of no load and low load can decrease the standby power

of the system, and improve the power convert efficiency.

The

internal synchronous

slope compensation, the

leading edge blanking function of the Sense pin not only

decrease the component number, but also improve the

stability of the system and avoid the harmonics generation.

WS2259 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 WS2259 is designed to be very low

（4uA） so that VDD could be charged up above UVLO

threshold level and 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

MΩ, 1/8 W could be used together with a VDD capacitor

to provide a fast startup and low power dissipation

solution.

Operating

Operating Current

Current

The operating current of WS2259 is very low .Good

efficiency is achieved with low operating current together

with extended burst mode control circuit which can easy

the design of VDD capacitor.

Soft-start

As soon as VDD reaches UVLO(on), the soft-start

function operates, the peak current is then gradually

increased from zero. Every restart attempt is followed by

4ms soft-start.

Burst

Burst Mode

Mode

At very light load or no load condition, the IC operates in

Burst Mode. In this condition, the voltage at FB is below

burst mode threshold level, thus system goes into burst

mode. The gate dive output switches only when VCC

voltage drops below a preset level or FB input is active to

output an on state. Otherwise the gate drive remains at off

state to minimize the switching loss thus reduce the

standby power consumption. The standby current of

WS2259 is low as 800uA, Thus the standby of WS2259

can be low than 100mW. The frequency control also

eliminates the audio noise at any loading conditions.

Oscillator

Oscillator Operation

Operation

A resistor connected between RI and GND sets the

charge/discharge time of the constant current source to

the internal cap and thus the PWM oscillator frequency is

determined. The relationship between RI and switching

frequency follows the below equation:

(

)

(

)

Khz

Kohm

6500

OSC =

If RI floating, the frequency will be internal set at 50 KHz

Current

Current Sensing

Sensing

Sensing and

and

and Leading

Leading

Leading Edge

Edge

Edge Blanking

Blanking

Cycle-by-Cycle current limiting is offered in WS2259. The

switch current is detected by a sense resistor into the

SENSE pin. The internal Leading-edge blanking chops off

the sense voltage spike at initial MOSFET on state due to

snubber diode circuit reverse recovery and thus reduce

the external RC filter circuit. The current limit comparator

is disabled and cannot turn off the external MOSFET

during the blanking period. PWM duty cycle is determined

by voltage level into SENSE pin and FB pin.

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 improves the close loop stability at CCM and

prevents the sub-harmonic oscillation and thus reduces

the output ripple voltage.

7/11

WS2259DP Datasheet(PDF) 7 Page - Shenzhen Winsemi Microelectronics Co., Ltd

WS2259DP Datasheet(HTML) 7 Page - Shenzhen Winsemi Microelectronics Co., Ltd

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