20160322030925 1441

WS9841 Product Description
WS9841 High Efficiency TRIAC dimmable LED
Driver
Features
Description

TRIAC dimmable

Internal 300V Power MOSFET
driver. The device operates in critical conduction mode and is

Critical Conduction Mode Operation
suitable for buck, buck-boost or fly-back LED lighting.

Ultra Low Operating Current

±5% LED Output Current Accuracy

LED Open Protection

LED Short Protection

Current Sensing Resistor Short Protection

VCC Under Voltage Protection

Thermal Regulation Function
the system reliability, including LED open circuit protection,

Available in SOP-8 Package
LED short circuit protection, VCC under voltage protection,
The WS9841 is a high efficiency TRIAC dimmable LED
The WS9841 integrates a 300V power MOSFET. It
utilizes patent pending MOSFET driving technique and
current sensing method. The operating current of the IC is
very low. With very few external components count, it can
achieve excellent constant current performance, so the
system cost and size are greatly reduced.
The WS9841 offers rich protection functions to improve
CS resistor short circuit protection and thermal regulation
function.
Typical Appliction

LED Candle Light

LED Bulb

Other LED Lighting
The WS9841 is available in a SOP-8 Package.
Typical Application Circuit
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WS9841 Product Description
Pin Definition and Device Marking
WS9841 is available in SOP-8 package:
WS9841S8P:Product Code
A:Product Code
X:Internal Code
BCY:Internal QC Code
YMX:D/C
Package Pin Definition
Pin name
Pin No.
Description
GND
1
Ground
VLN
2
Line Voltage Detecting Pin
FB
3
Over Voltage Protection Detecting Pin.
VCC
4
Power Supply Pin
DRAIN
5,6
Internal HV Power MOSFET Drain.
CS
7,8
Current Sense Pin. Connect a sensing resistor between this pin and GND pin.
Block Diagram
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WS9841 Product Description
Ordering Information
Package
Marking
Part Number
8-Pin SOP-8, Pb-free
WS9841S8P
WS9841S8P
Absolute Maximum Ratings
Symbol
Parameter
Limit
Unit
ICC_MAX
VCC pin maximum sink current
10
mA
DRAIN
Internal HV MOSFET drain voltage
-0.3~300
V
CS
Current sense pin input voltage
-0.3~6
V
FB
Over voltage protection detecting pin voltage
-0.3~6
V
VLN
Line voltage detecting pin voltage
-0.3~6
V
PDMAX
Power dissipation (note 2)
0.45
W
θJA
Thermal resistance (Junction to Ambient)
145
℃/W
TJ
Operating junction temperature
-40 to 150
℃
TSTG
Storage temperature range
-55 to 150
℃
ESD (note 3)
2
KV
Note 1: Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. Under
“recommended operating conditions” the device operation is assured, but some particular parameter may not be achieved.
The electrical characteristics table defines the operation range of the device, the electrical characteristics is assured on DC and
AC voltage by test program. For the parameters without minimum and maximum value in the EC table, the typical value defines
the operation range, the accuracy is not guaranteed by spec.
Note 2: The maximum power dissipation decrease if temperature rise, it is decided by TJMAX, θ JA, and environment
temperature (TA). The maximum power dissipation is the lower one between PDMAX = (TJMAX - TA)/ θ JA and the number
listed in the maximum table.
Note 3: Human Body mode, 100pF capacitor discharge on 1.5KΩ resistor
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WS9841 Product Description
Electrical Characteristics
Conditions: (Notes 4, 5) (Unless otherwise specified, VCC=15V and TA =25 ℃)
Parameter
Symbol
Condition
Min.
Typ.
Max.
Unit
VCC Clamp Voltage
VCC_CLAMP
1mA
18.8
V
VCC Turn On Threshold
VCC_ON
VCC Rising
14
V
VCC Turn off Threshold
VCC_UVLO
VCC Falling
8.8
V
VCC Startup Current
IST
VCC= VCC-ON - 1V
120
180
uA
VCC Operating Current
IOP
FOP=70KHz
90
150
uA
400
420
mV
Supply Voltage Section
Current Sense Section
Threshold Voltage for Peak
VCS_TH
Current Limit
380
Threshold Voltage for Peak
Current Limit When Output
VCS_SHORT
Output Short
200
mV
TLEB
350
ns
TDELAY
200
ns
VVLN_TH
3
V
Minimum OFF Time
TOFF_MIN
2.5
us
Maximum OFF Time
TOFF_MAX
250
us
Maximum On Time
TON_MAX
10
us
VFB_OVP
1
V
3
Ω
Short
Leading Edge Blanking Time
for Current Sense
Switch Off Delay Time
Line Voltage Feed Forward
Threshold
Internal Time Control Section
Over Voltage Protection Section
FB Over Voltage Protection
Threshold
MOSFET Section
Static Drain-source
On-resistance
Drain-Source Breakdown
Voltage
Power MOSFET Drain Leakage
Current
RDS_ON
VGS=15V/IDS=0.5A
BVDSS
VGS=0V/IDS=250uA
IDSS
VGS=0V/VDS=300V
300
V
1
uA
Thermal section
Thermal Regulation
TREG
Temperature
150
℃
Note 4: production testing of the chip is performed at 25°C.
Note 5: the maximum and minimum parameters specified are guaranteed by test, the typical value are guaranteed by design,
characterization and statistical analysis.
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WS9841 Product Description
Function Description
The WS9841 is a high efficiency TRIAC dimmable LED
driver IC, specially designed for Buck, Buck-boost or
Fly-back LED lighting. The WS9841 integrates a 300V power
MOSFET. Utilizing patent pending MOSFET source driving
technique, it can achieve excellent constant current
performance with very few external components count, so
the system cost and size are 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 WS9841 integrates an 18.8V zener
diode to clamp the VCC voltage. After the output voltage is
established, VCC is supplied by the output voltage.
Figure 5. Relationship of VLN voltage and VCS_TH
Inductor Selection
The WS9841 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:
Constant Current Control
t on 
Cycle by Cycle current sense is adopted in WS9841, 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.
Where,
L is the inductance value.
VIN is the DC bus voltage after the rectifier bridge.
The peak inductor current is given by:
I PK 
L  IPK
VIN  VLED
VLED is the voltage on the LED.
400
(mA)
R CS
The maximum on time of the MOSFET is set to 10us
internally.
Where, RCS is the current sense resistor value. The CS
comparator includes a 350ns leading edge blanking time.
The VLN pin detects the TRIAC dimmer conducting
angle to adjust the LED driver output current. The application
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:
circuit of the VLN pin is shown in Figure 4. When the VLN pin
t off 
voltage is higher than 3V, the threshold for peak current limit
VCS_TH decreases linearly as shown in Figure 5. When the
VLN pin is not used, it can be grounded or floated.
L  IPK
VLED
The inductance can be calculated by the equation:
L
VLED  (VIN  VLED )
f  IPK  VIN
Where, f is the maximum 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.
Figure 4. VLN pin application circuit
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WS9841 Product Description
Over Voltage Protection
gradually reduced; the output power and thermal dissipation
The FB pin is used to detection the output voltage for
are also reduced. The system temperature is regulated and
over voltage protection (OVP). The FB pin threshold is 1V.
the system reliability is improved. The thermal regulation
The resistor divider of the FB pin can be set as:
temperature is set to 150℃ internally.
RFBL
1

RFBL  RFBH VOVP
PCB Layout
The following rules should be followed in WS9841 PCB
layout:
Where,
Bypass Capacitor
RFBL is the lower resistor of the resistor divider
The bypass capacitor on VCC pin should be as close as
RFBH is the higher resistor of the resistor divider
possible to the VCC Pin and GND pin.
VOVP is the over voltage protection set value.
FB Pin
For maximizing the system efficiency, the lower resistor
The feedback resistor divider should be as close as
is recommended to be around 5KΩ.
possible to the FB pin, and the trace must keeps away from
dynamic node of the inductor and Drain pin trace, otherwise
Protection Function
the FB pin OVP function might have risk to be mis-triggered by
The WS9841 offers rich protection functions to improve
the system noise.
the system reliability, including LED open/short protection,
VLN Pin
CS resistor short protection, VCC under voltage protection,
The VLN pin resistor divider and capacitor should be as
thermal regulation.
close as possible to the VLN pin, and the VLN node should be
When the LED is open circuit, the system will trigger the
away from the high voltage switching nodes.
over voltage protection and stop switching.
Ground Path
When the LED short circuit is detected, the system
The power ground path for current sense resistor should
works at low frequency (4kHz), and the CS pin turn off
be short and wide, and it should be as close as possible to the
threshold is reduced to 200mV. So the system power
IC GND pin. The IC signal ground for FB resistors should be
consumption is very low. At some catastrophic fault condition,
connected to the IC GND pin with short traces and should be
such as CS resistor shorted or inductor saturated, the
away from the power ground path.
internal fast fault detection circuit will be triggered, the
The Area of Power Loop
system stops switching immediately.
The area of main current loop should be as small as
After the system enters into fault condition, the VCC
voltage will decrease until it reaches the UVLO threshold,
possible to reduce EMI radiation, such as the power MOSFET,
the output diode and the bus capacitor loop.
then the system will re-start again. If the fault condition is
DRAIN Pin
removed, the system will recover to normal operation.
To increase the copper area of DRAIN pin for better
thermal dissipation. However, too large copper area may
Thermal Regulation
compromise the EMI performance.
The WS9841 integrates thermal regulation function.
When the system is over temperature, the output current is
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WS9841 Product Description
SOP8 Package Dimension
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Dimensions in Millimeters
Symbol
Dimensions in Inches
Min
Max
Min
Max
A
4.70
5.10
0.185
0.201
B
3.70
4.10
0.146
0.161
C
1.30
1.50
0.051
0.059
A1
0.35
0.48
0.014
0.019
A2
1.27TYP
0.05TYP
A3
0.345TYP
0.014TYP
B1
5.80
B2
6.20
0.228
5.00TYP
0.244
0.197TYP
C1
0.55
0.70
0.022
0.028
C2
0.55
0.70
0.022
0.028
C3
0.05
0.225
0.002
0.009
C4
0.203TYP
0.008TYP
D
1.05TYP
0.041TYP
D1
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WS9841 Product Description
NOTE:
1.We strongly recommend customers check carefully on the trademark when buying our product, if there is any
question, please don't be hesitate to contact us.
2.Please do not exceed the absolute maximum ratings of the device when circuit designing.
3.Winsemi Microelectronics Co., Ltd reserved the right to make changes in this specification sheet and is
subject to change without prior notice.
CONTACT:
Winsemi Microelectronics Co., Ltd.
ADD:Futian District, ShenZhen Tian An Cyber Tech Plaza two East Wing 1002
Post Code : 518040
Tel : +86-755-8250 6288
FAX : +86-755-8250 6299
Web Site : www.winsemi.com
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