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PDF WS3441A Data sheet ( Hoja de datos )

Número de pieza WS3441A
Descripción Non-isolated Buck Offline LED Driver
Fabricantes WINSEMI 
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WS3441A Hoja de datos, Descripción, Manual
WS3441A ProductDescription
Features
Critical Conduction Mode Operation
Internal 500V Power MOSFET
No Auxiliary Winding
Ultra Low Operating Current
±3% LED Output Current Accuracy
Efficiency up to 93%
LED Open Protection
LED Short Protection
Current Sensing Resistor Short Protection
Thermal Regulation Function
Available in SOP-8 Package
Applications
LED Candle Light
LED Bulb, Spot Light
T8/T10 LED String
Other LED Lighting
Typical Application
Non-isolated Buck Offline LED Driver
Description
The WS3441A is a high precision buck constant current
LED driver. The device operates in critical conduction mode
and is suitable for 85Vac~265Vac universal input offline LED
lighting.
The WS3441A integrates a 500V power MOSFET. The
operating current of the IC is very low. So it doesn’t need the
auxiliary winding for supplying the chip. It can achieve
excellent constant current performance with very few external
components, so the system cost and size are minimized.
The WS3441A utilizes patent pending current control
method. It can achieve precise output current and excellent
line regulation. The driver operates in critical conduction
mode, the output current does not change with the inductance
and LED output voltage.
The WS3441A offers rich protection functions to improve
the system reliability, including LED open circuit protection,
LED short circuit protection, VCC under voltage protection,
CS resistor short circuit protection and thermal regulation
function.
The WS3441A is available in SOP-8 Package.
AttentionA 22pF capacitor can be parallel with Rovp and a resistor can be parallel with the Vcc capacitor.
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
Copyright@WinsemiMicroelectronics Co.,Ltd.,All rightreserved
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
1105

1 page

WS3441A pdf
WS3441A ProductDescription
Application Information
The WS3441A is a high performance non-isolated Buck
converter specially designed for LED lighting. The device
t on
L IPK
VIN VLED
integrates a 500V power MOSFET. With very few external
Where,
components, the converter achieves excellent constant
L is the inductance value
current control. And it does not need auxiliary winding for
VIN is the DC bus voltage after the rectifier bridge
powering the IC or voltage sensing, hence the system size
VLED is the voltage on the LED
and cost is greatly reduced.
After the power MOSFET is switched off, the current in
Start Up
the inductor decreases. When the inductor current reaches
zero, the power MOSFET is turned on again by IC internal
After system powered up, the VCC pin capacitor is
logic. The off time of the MOSFET is given by:
charged up by the start up resistor. When the VCC pin
voltage reaches the turn on threshold, the internal circuits
start operating. The WS3441A integrates a 17V zener diode
t off
L IPK
VLED
to clamp the VCC voltage. Due to the ultra-low operating
The inductance can be calculated by the equation:
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
L
VLED
f
(VIN VLED )
IPK VIN
can be be calculated by the equation:
The f is the system switching frequency, which is
Rst
Vin _ min 1.414
I st _ max
176V 1.414
270uA
920k
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 WS3441A is set
Constant Current Control
Cycle by Cycle current sense is adopted in WS3441A,
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:
I PK
400
R CS
(mA)
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
Where, RCS is the current sense resistor value.
The current in LED can be calculated by the equation:
I LED
I PK
2
Where, IPK is the peak current of the inductor.
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:
Inductor Selection
The WS3441A 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:
Tovp
L Vcs
Rcs Vovp
Where
Vcs is the CS pin turn off threshold (400mV)
Vovp is the open circuit protection voltage
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
www.winsemi.com Tel : +86-755-8250 6288 Fax : +86-755-8250 6299
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
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