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WS3442A
Constant Current Controller for Non-isolated Buck LED Driver
Features
General Description
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Inductor Current Critical Mode, No Need to
The WS3442A is a high precision constant current
Compensate the Inductance Variation
controller,designed for non-isolated buck LED driver. It
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550V MOSFET integrated
can operate under universal AC input or 12V~550V DC
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Source Driver Structure, Not Need the Auxiliary
input.
Winding for VCC
The WS3442A integrates 550V power MOSFET, so it can
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±3% LED Current Accuracy
achieve excellent constant current performance with very
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Up to 93% System Efficiency
few external components.
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LED Open/Short Circuit Protection
The WS3442A uses high precision current sense circuit
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Current Sense Resistor Short Circuit Protection
and patent method for constant current control, to achieve
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Over Temperature Protection
high precision output current and excellent line regulation.
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Programmable LED open protection
The WS3442A operates in inductor current critical mode.
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Frequency shuffling
The LED current is constant over wide range of
inductance variation and the LED output voltage, so the
Applications
load regulation is excellent.
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LED Bulb
The WS3442A uses patent source driver architecture. The
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LED Candle light
operation current is 200uA only, so the auxiliary winding is
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LED Spot light
not needed. It can simplify the system design and reduce
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Decorative LED lighting
the system cost.
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T5/T8 Lamp
The WS3442A offers rich protection functions, including
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Ceiling Lamp
LED open/short circuit protection, current sense resistor
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Flat Lamp
short circuit protection and over temperature protection.
Typical Application Circuit
AC
1 G ND
CS
8
2 ROV P
CS
7
3 VCC
D R A IN
6
4 S O URCE
D R A IN
5
W/T-DS028-Rev.A/ 0 Nov.2013
[email protected] Microelectronics Co., Ltd., All right r eserved.
1113
WS3442A
Pin Definition and Device Marking
WS3442A is available in DIP-8 package.
1
RO VP
2
VCC
3
So u rc e
4
WS3442AD8P
AXB YM
GND
8
CS
7
CS
WS3442AD8P: Product code
A: Product Code
X:Internal Code
6
D R A IN
B:Area Code
5
D R A IN
YM:Year, Month
Pin Function Description
Pin Name
Pin NO.
Description
GND
1
Ground
ROVP
2
Programmable LED open protection pin,connect a resistor to GND
VCC
3
Power supply
Source
4
Source driver output, connect to the source of power-mos
DRAIN
5,6
Internal HV power MOSFET drain
CS
7,8
Current sense input, the sense resistor is connected from CS to ground
Block Diagram
VCC
3
D r a in
5 ,6
Soft-Driver
GND
1
UVLO
Inter
s upply
Zero-Current
Detec t
400mV
L in e
c ompens ation
OCP
4 So u r c e
L o g ic
&
dr iv er
CS Shor t
RO VP 2
L ED OPEN
PR O TEC TIO N
LED Shor t
O TP
CS
7 ,8
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WS3442A
Ordering Information
Package
Part Number
Marking
8-Pin DIP-8, Pb-free
WS3442AD8P
WS3442AD8P
Recommended Operating Condition
symbol
symbol
parameter
value
units
WS3442A
P
output power
< 28
W
Absolute Maximum Ratings
symbol
parameter
Range
Units
VDS
I CC_MAX
Internal HV MOSFET drain voltage
-0.3~550
V
VCC pin maximum sink current
2.5
mA
VROVP
VCS
ROVP input voltage
-0.3~7
V
Current sense pin input voltage
-0.3~7
V
PDMAX
TJ
Power dissipation
0.9
W
Operating junction temperature
150
℃
TSTG
Storage temperature range
-55~150
℃
Note: 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.
3/7
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WS3442A
Electrical Characteristics (Unless otherwise specified,TA=25℃,VCC=16V)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Supply Voltage Section
Vcc_clamp
VCC Clamping Voltage
-
18
-
V
Icc_clamp
VCC Clamping Current
-
-
2.5
mA
VCC_ST
VCC Start Up Voltage
12
13.1
14.5
V
VCC Falling
-
4.3
-
V
VCC<VCC_ST-0.5V
-
-
50
uA
-
200
-
uA
390
400
410
mV
Vuvlo_HYS
VCC Rise
VCC Under Voltage
Latch Out Hysteresis
Ist
Start Up Current
Iop
Operation Current
Current Sensor Section
Vcs_th
Current Sensor Voltage
Threshold
TLEB
Leading Edge Blanking
-
350
-
ns
TDELAY
Turn Off Delay Time
-
300
-
ns
Internal Driver Section
TOFF_MIN
Minimum Demagnetization Time
-
4
-
us
TOFF_MIN
Maximum Demagnetization Time
-
130
-
us
TON_MAX
Maximum Turn On Time
-
40
-
us
-
-
6.5
ohm
550
-
-
V
Internal HV MOSFET
RDSON
Switch ON Resistance
VGS =10V,I D=1.0A
VDS_BD
Drain to Source voltage
I D=250μA
Over Temperature Section
TSD
Thermal Shut Down Temperature
-
150
-
℃
TSD_HYS
Thermal Shut Down Hysteresis
-
30
-
℃
4/7
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WS3442A
The IPK is the peak current in inductor.
Function Description
WS3442A is a constant current controller, designed for
driving non-isolated buck LED power supply. WS3442A
Line Compensation
integrates 550V power MOSFET, and it uses patent
constant current control method and source driver
The WS3442A integrates line compensation function.
structure, excellent constant current characteristic is
Excellent line regulation is achieved.
achieved with low counts components. Low cost and
high efficiency of system is realized.
Source Driver Structure
Start up
The WS3442A uses the patent source driver structure.
The typical operation current is as low as 200uA, the
The Vcc will be charged through the startup resistor
auxiliary winding is not need. So the system design is
when the system is powered on. When the voltage on
simple and the cost is low.
Vcc reaches the startup voltage threshold, the controller
starts to switching. The Vcc voltage of WS3442A is
clamped to 1 8V by internal Zener diode.
Inductance Calculation
Constant
The WS3442A is designed to work in inductor current
Current Control and
Output Current
critical mode, the energy will be stored in the inductor
Setting
when the MOSFET is turned on. The turn on time is
The WS3442A uses patent constant current control
method, excellent constant current is achieved with low
counts components. The WS3442A senses the peak
current in inductor cycle by cycle. The CS Pin is
connected to the input of internal current comparator,
and compared with the internal 400mV reference voltage.
The external power MOSFET will be turned off when the
CS pin voltage reaches the voltage threshold. The
comparator has a 350ns LEB timer to avoid mis-trigger.
given by:
t on =
L × I PK
VIN − VLED
The L is the inductance. The Ipk is the peak current in
inductor. The VIN is the input rectified voltage. The VLED
is the voltage on LED.
When the power MOSFET is turned off, the inductor
current will decrease from the peak current to zero. The
turn off time is given b y:
The peak current in the inductor is given by:
I PK
t off =
400
=
( mA)
RCS
The Rcs is the resistance of current sense resistor The
current in LED can be calculated by the following
The MOSFET will be turned on again when it detects the
inductor current goes to zero. The inductance can be
calculated by the following equation:
equation:
I LED =
L × I PK
VLED
I PK
2
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WS3442A
L=
VLED × (VIN − VLED )
f × I PK × VIN
In which the Vcs is the OCP threshold (0.4V) ,the Vovp is
The f is the system switching frequency, which is
the new target output protection voltage. And the value
of the resistor Rovp is as below:
proportional to the input voltage. So the minimum
switching frequency is set at lowest input voltage, and
maximum switching frequency is set at highest input
Rovp = 15 * Tovp * 10 6
(KΩ)
Protection Functions
voltage.
The WS3442A internally set the minimum off time to 4us
and maximum off time to 130us. When the inductance is
very small, the toff may goes below the minimum off time
and the inductor current becomes discontinuous. So the
output LED current will be smaller than the setting value.
If the inductance is too large, the toff may goes beyond
the maximum off time and the inductor current becomes
continuous. And the output LED current will be larger
than the setting value. So it’s very important to select a
The WS3442A has many protection functions, including
LED open/short circuit protection, current sense resistor
short circuit protection and over temperature protection.
All of the
protection functions
are designed to
auto-recover. The over temperature protection circuitry in
the WS3442A monitors the die junction temperature after
start up. When the temperature rises to 150℃, the power
MOSFET will be shut down immediately and maintains
at switch off condition until the temperature on die falls
right inductance.
The WS3442A also internally set the maximum on time
30℃ below the thermal protection trigger point.
to 40us. When the input voltage is very low or LED
output voltage is very high, the ton may goes beyond the
PCB Layout
maximum on time. The power MOSFET will be turned off
even the inductor current still below the setting value. So
the output LED current will be smaller than the setting
The following guidelines should be followed in WS3442A
PCB layout:
Bypass Capacitor
value.
The bypass capacitor on VCC pin should be as close as
possible to the VCC and GND pins.
Set open protection
Ground Path
The LED open protection voltage can be set by adjusting
the value of the resistor connecting from ROVP to GND.
The power ground path for current sense should be short,
and the power ground path should be separated from
small signal ground path before the negative node of the
Rovp voltage is 0.5V.
In the LED open condition, the output voltage will raise
graduate, and the demagnetize time will shorten as well,
the demagnetize time Tovp can be calculator as below:
bus capacitor.
The Area of Power Loop
The area of main current loop should be as small as
possible to reduce EMI radiation. And the controller
L × V CS
Tovp =
R CS × V OVP
(KΩ)
should be placed away.
from the heat generator, such as the power diode.
6/7
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WS3442A
Package Information
DIP-8 Package Outline Dimensions
D2
θ1
C1
C
C4
θ2
C2
C3
θ3
A2
A5
A1
D1
A3
D
A4
B
A
Winsemi
Symbol
Dimensions in Millimeters
Dimensions in Inches
Min
Max
Min
Max
A
9.00
9.50
0.354
0.374
B
6.10
6.60
0.240
0.260
C
3.0
3.4
0.118
0.134
A1
1.474
1.574
0.058
0.062
A2
0.41
0.53
0.016
0.021
A3
2.44
2.64
0.096
0.104
A4
0.51TYP
0.02TYP
A5
0.99TYP
0.04TYP
C1
6.6
C2
7.30
0.260
0.50TYP
0.287
0.02TYP
C3
3.00
3.40
0.118
0.134
C4
1.47
1.65
0.058
0.065
D
7.62
9.3
0.300
0.366
D1
0.24
0.32
0.009
0.013
D2
7.62TYP
0.3TYP
W/T-DS028-Rev.A/ 0 Nov.2013
[email protected] Microelectronics Co., Ltd., All right r eserved.
1113