WS3443 datasheet(5/8 Pages) WINSEMI

5 / 8 page

WS3443 ProductDescription

WINSEMI MICROELECTRONICS

www.winsemi.com Tel : +86-755-8250 6288

Fax : +86-755-8250 6299

5/8

Application Information

The WS3443 is a high performance non-isolated Buck

converter specially designed for LED lighting. The device

integrates a 500V power MOSFET. With very few external

components, the converter achieves excellent constant

current control. And it does not need auxiliary winding for

powering the IC or voltage sensing, hence the system size

and cost is greatly reduced.

Start Up

After system powered up, the VCC pin capacitor is

charged up by the start up resistor. When the VCC pin

voltage reaches the turn on threshold, the internal circuits

start operating. The WS3443 integrates a 17V zener diode

to clamp the VCC voltage. Due to the ultra-low operating

current, the auxiliary winding is not needed to supply the IC.

The maximum value of the startup current is 270uA. For

the application of 176VAC — 264VAC, the startup resistor

can be be calculated by the equation:

_ min

_ max

1.414 176

1.414

920k

270











Constant Current Control

Cycle by Cycle current sense is adopted in WS3443,

the CS pin is connected to the current sense comparator,

and the voltage on CS pin is compared with the internal

400mV reference voltage. The MOSFET will be switched off

when the voltage on CS pin reaches the threshold. The CS

comparator includes a 350ns leading edge blanking time.

The peak inductor current is given by:

)

(

400

PK 

Where, RCS is the current sense resistor value.

The current in LED can be calculated by the equation:

LED 

Where, IPK is the peak current of the inductor.

Inductor Selection

The WS3443 works under inductor current critical

conduction mode. When the power MOFET is switched on,

the current in the inductor rises up from zero, the on time of

the MOSFET can be calculated by the equation:

LED







Where,

L is the inductance value

VIN is the DC bus voltage after the rectifier bridge

VLED is the voltage on the LED

After the power MOSFET is switched off, the current in

the inductor decreases. When the inductor current reaches

zero, the power MOSFET is turned on again by IC internal

logic. The off time of the MOSFET is given by:

LED

off





The inductance can be calculated by the equation:

LED

)

(









The f is the system switching frequency, which is

proportional to the input voltage. So the minimum switching

frequency is set at lowest input voltage, and the maximum

switching frequency is set at highest input voltage.

The minimum and maximum off time of WS3443 is set

at 3us and 340us, respectively. Referring to the equation of

Toff calculation, if the inductance is too small, the Toff may

be smaller than the minimum off time, system will operate in

discontinuous conduction mode and the output current will

be smaller than the designed value. If the inductance is too

large, the Toff may be larger than the maximum off time, the

system will operate in continuous conduction mode and the

output current will be higher than the designed value. So it is

important to choose a proper inductance.

Over Voltage Protection

The over voltage protection can be programmed by the

ROVP pin resistor. The ROVP pin voltage is 0.5V.

When the LED is open circuit, the output voltage

increases gradually, and the demagnetization time gets

shorter. The demagnetization time at OVP---- Tovp can be

calculated by the open circuit protection voltage:

Vovp

Rcs

Vcs

Tovp





Where，

Vcs is the CS pin turn off threshold (400mV)

Vovp is the open circuit protection voltage

WS3443 Scheda tecnica(PDF) 5 Page - Shenzhen Winsemi Microelectronics Co., Ltd

WS3443 Scheda tecnica(HTML) 5 Page - Shenzhen Winsemi Microelectronics Co., Ltd

Html Pages

1 2 3 4 5 6 7 8

Scheda tecnica Scarica

Link URL