BW7381

BW7381
Universal High Brightness LED Driver
Description
Packing & Order Information
The BW7381 is a controller for off-line LED converter.
3,000/Reel
The BW7381 operate with constant off-time, peak
current mode control with active power factor correction
function. The controller senses real-time switch current
to cycle-by-cycle current limit. Cycle-by-cycle current
limit at the CS pin ensure a safe operation during
short-circuit at the output. It can be configured in either
SOP-8 PACKAGE OUTLINE
buck-boost (Figure1) or buck (Figure2) application
circuit. The driver output voltage is limited to 19V to
protect external power MOSFET. The controller also
monitors integrated actual LED current to perform the
excellent line and load regulation. The controller makes
the inductor current to follow the shape of input voltage
to perform high power factor and low THD solution.
The BW7381 provides complete protection features such
as short-circuit and open-circuit protection.
Features
• Universal Rectified 90VAC to 264VAC Input Voltage
Range
• Built-in Active Power Factor Correction Technique
Pin Configurations (Top View)
• Low THD, meet with IEC-61000-3-2 Class-C
• High Efficiency Application
• Built-in Output Short Circuit Protection with
Auto-Recovery
• Built-in Output Over Voltage Protection with
Auto-Recovery
• Built-in Gate Clamp
• Cycle-by-cycle Current Limit
• Fail-Safe, Output is not subjected to line voltage if the
MOSFET fails.
Applications
• Excellently Accurate Constant Current
• LED lighting
• Very Tight Line and Load Regulation
• Down light
• Constant Off-Time
• Tube lamp
• Buck or Buck-Boost Configuration
• PAR lamp
• Bulb
Publication Order Number: [BW7381]
© Bruckewell Technology Corporation Rev. A -2014
BW7381
Universal High Brightness LED Driver
PIN DESCRIPTIONS
Pin Name
Pin Description
CS
Switch current sense pin.
GND
IC ground and reference.
FLT
Actual output current sensing pin.
COMP
Output pin of error amplifier.
RT
Efficiency / THD option pin
VIN
AC-Line voltage sensing pin.
VDD
Power supply pin for all internal circuit.
OUT
Power MOSFET driver output.
TYPICAL APPLICATION CIRCUITS
Buck-Boost Topology
Figure 1
Publication Order Number: [BW7381]
© Bruckewell Technology Corporation Rev. A -2014
BW7381
Universal High Brightness LED Driver
Buck Topology
Figure 2
ABSOLUTE MAXIMUM RATINGS (Note 1)
Parameter
Symbol
Range
Unit
Power supply pin
VDD
-0.3 to 30
V
CS voltage to GND
VCS
-0.3 to 5
V
FLT voltage to GND
VFLT
-0.3 to 5
V
VCOMP
-0.3 to 5
V
VIN voltage to GND
VIN
-0.3 to 5
V
RT voltage to GND
VRT
-0.3 to 5
V
OUT voltage to GND
VOUT
-0.3 to 30
V
Operating junction temperature rang
TJ
-40 to +150
°C
Operating ambient temperature rang
TOPA
-40 to +85
°C
Storage temperature rang
TSTG
-65 to +150
°C
Lead temperature (Soldering 10 sec)
TLEAD
260
°C
COMP voltage to GND
Publication Order Number: [BW7381]
© Bruckewell Technology Corporation Rev. A -2014
BW7381
Universal High Brightness LED Driver
ABSOLUTE MAXIMUM RATINGS (Note 1)
Parameter
Symbol
Range
Unit
Power dissipation @TA=25°C
PD
0.4
W
Thermal resistance junction to ambient (Note 2)
θJA
220
°C/W
VESD
2
kV
ESD rating, Human body mode (Note 3)
RECOMMENDED OPERATING CONDITIONS (Note 4)
Parameter
Symbol
Operation Conditions
Unit
VDD
20
V
Junction Temperature Range
TJ
-20 to +125
°C
Ambient Temperature Range
TA
-20 to +85
°C
Supply Voltage
Note 1: Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the
device. These are for stress ratings. Functional operation of the device at these or any other conditions
beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods may remain possibility to affect device reliability.
Note 2: Thermal Resistance is specified with the component mounted on a low effective thermal
conductivity test board in free air at TA=25°C.
Note 3: Devices are ESD sensitive. Handing precaution recommended.
Note 4: The device is not guaranteed to function outside its operating conditions.
BLOCK DIAGRAM
Figure 3
Publication Order Number: [BW7381]
© Bruckewell Technology Corporation Rev. A -2014
BW7381
Universal High Brightness LED Driver
ELECTRICAL CHARACTERISTICS TA= 25°C, unless otherwise specified.
VDD SECTION
Parameter
Symbol
Start-up Threshold
Min
Typ.
Max.
Units
VDD(ST)
17
18
19
V
Under Voltage Lockout Threshold
VDD(UVLO)
7.5
8.5
9.5
V
Over Voltage Protection
VOVP
27
28
29
V
Start-up Current
IINST
42
60
78
uA
Operating Current
IDDQ
560
800
1040
uA
CURRENT LIMIT SECTION
Parameter
Symbol
Min
Typ.
Max.
Units
Maximum Current Sense Voltage
VCSPK
0.67
0.7
0.74
V
Propagation Delay
TDLY
ERROR AMPLIFIER SECTION
Parameter
Symbol
Transconductance
GM
Maximum Sink Current
ISINK
53
uA
Maximum Source Current
ISOURCE
58
uA
LINE SENSING SECTION
Parameter
Symbol
Source Current
ISE(VIN)
VDD(ST) - 1V
Conditions
70
OUTPUT CURRENT INTEGRATION
Parameter
Symbol
Reference Voltage
Conditions
Conditions
Conditions
Conditions
Min
Typ.
Max.
Units
84
120
156
uS
Min
Min
Typ.
Typ.
Max.
Units
375
uA
Max.
Units
0.2
VIREF
CONSTANT OFF TIME SECTION
Parameter
Symbol
ns
Conditions
V
Min
Typ.
Max.
Units
0.95
1
1.05
V
40.4
us
Regulated Voltage
VRT
Off-time Setting Range
TOFF
RRT = 136K~17K
5.73
TOFF(LV)
RT = 50K, 85Vac~150Vac
13.5
15
16.5
us
TOFF(HV)
RT = 50K, 180Vac~300Vac
18.9
21
23.1
us
DRIVER SECTION
Parameter
Symbol
Conditions
Min
Typ.
Max.
Units
Rising Time
TRISE
VDD=12V, C_load=1nF
48
ns
Falling Time
TFAIL
VDD=12V, C_load=1nF
31
ns
Clamped Voltage
VGATE
Constant Off-Time
Publication Order Number: [BW7381]
19
V
© Bruckewell Technology Corporation Rev. A -2014
BW7381
Universal High Brightness LED Driver
APPLICATION INFORMATION
2. Pin Detail
1. Function Description
2-1. CS
The BW7381 is a high performance controller which monitors
MOSFET current sensing, use for cycle by cycle switch peak
actual output current. These results BW7381 enable tight line
current control.
and load regulation. The BW7381 uses constant off-time peak
current mode control to control the switching current in the
MOSFET.
At Initial, VDD capacitor charged through start-up resistor until it
2-2. GND
achieves 18V. Then BW7381 turns-on the MOSFET and make
GND is the reference node of internal circuit.
its shape of peak current flow input sine wave. This performs
2-3. FLT
high power factor and low total harmonic distortion. The output
Actual output current sensing, the signal feedback to error
current flow through a current sensing resistor and feedback to
amplifier and compare with the internal reference voltage (0.2V).
FLT pin. The controller always adjusts the amplitude of current
command base on the potential of FLT pin. Once the peak
current reaches the current command, controller turns off the
MOSFET. The resistor connected at RT pin determines the
2-4. COMP
off-time. At the switching on-time, controller senses and limits the
This is the output of the Gm amplifier. Connect with a suitable
maximum switch current by CS pin. This ensures the current in
RC network to ground.
MOSFET be limited in safe operating area.
2-5. RT
Constant off-time setup.
The BW7381 built-in output short-circuit and over-voltage
For low-line, 85Vac to 150Vac
protection. While the MOSFET turns off at the off-time, the VDD
capacitor can get charge by output voltage, and controller can
set output over voltage protection threshold by specified zener
diode. If the LED string is open, the output voltage will be boost
For high-line, 180 to 300Vac
over the designed level until the VDD arrive to 28V. The
BW7381 goes into over-voltage protection and latches the
MOSFET. The controller starts up the system again while the
VDD falls to 8.5V (UVLO). Therefore, the converter
2-6. VIN
auto-recovery output while the output open circuit condition
Sense signal input from the rectified line voltage.
removed. In case of output short-circuit condition. The VDD
2-7. VDD
capacitor cannot get charge from output voltage. So, the
Power supply for the controller during normal operation. The
converter repeats start-up and UVLO. However, the BW7381
controller will start up when VDD reaches 18V (typical) and will
provides full protections such as OCP, OVP, gate-voltage clamp
shut-down when VDD voltage is below 8.5V (typical). A
and cycle-by-cycle current limit.
decoupling capacitor should be connected between the VDD
and GND pin as close as possible.
Publication Order Number: [BW7381]
© Bruckewell Technology Corporation Rev. A -2014
BW7381
Universal High Brightness LED Driver
2-8. OUT
Gate drive for external MOSFET switch.
3. Design Flow
3-6. VDD, Supply Current Circuit
The typical application circuit for design flow below please refers
At the beginning in start-up, the output voltage is not high
to figure 1.
enough to charge VDD capacitor. Therefore VDD capacitor
3-1. Input Signal Sampling
have to save enough energy for IC operating bias during
The BW7381 sense input signal from rectified line voltage. VIN
start-up. To determine the capacitance, we need to calculate the
pin in series with a resistor of 1.6M, R7 to system ground. It is
IC operating current, IDD first.
need to pay attention to enough voltage rating for resistor
In general, assume the VDD capacitor need to keep enough
3-2. Low Pass Filter for Switch and Output Current Sensing
energy for 50ms. Then the capacitance can be calculated.
Two R-C low pass filter are must for MOSFET switch current
sensing and actual output current sensing. The following is
recommend values :
Place the VDD capacitor C2 and bypass capacitor C3 as close
to IC as possible. Morevoer,a current spike filter resistor R11 is
suggest (10Ω ~22Ω) to place between VDD and C3.
3-7. Start-up Resistor
At the initial stage, the VDD capacitor get charge through
start-up resistor towards the start-up threshold voltage. The
smaller start-up resistor the larger power dissipation. The larger
3-3. Loop Compensation
start-up resistor the longer charge time.
Place a capacitor of 2.2uF for compensation is recommend.
3-4. Output Current Sensing Resistor
The output current can be set up by a current sensing resistor,
3-8. Off-Time setting
R2. The resistance is calculated following the equation below.
The duty cycle in buck-boost converter is a function of Vin and
Vo.
3-5. OVP Threshold Voltage
The BW7381 perform output over voltage protection though
The off-time can be set manually by adjusting the size of an
VDD pin. Once VDD pin exceed in 28V, BW7381 turns off and
external resistor (RT). The BW7381 automaticall adjusts the
latch out the MOSFET switcher. The OVP threshold voltage can
off-time with the line voltage (Vac). To calculat the operating
be set by the Zener diode, ZD1.
off-time and RT, the maximum switching frequency at peak of
Publication Order Number: [BW7381]
© Bruckewell Technology Corporation Rev. A -2014
BW7381
Universal High Brightness LED Driver
line cycle must be determined first.
inductor must ensure that there is a sufficient flux density margin
to avoid saturation with operating current being applied.
3-10. Switch Current Sensing Resistor
The BW7381 sense switch current from CS pin to provide
cycle-by-cycle current limit. While the CS pin goes execss of
700mV, the BW7381 force MOSFET switcher turn off. Design
the peak inductor current to 75 percent of switcher current limit is
recommend.
where :
toffH is the off-time at high-line (180Vac to 300Vac),
toffL is the off-time at low-line (90Vac to 135Vac),
3-9. Power Inductor
Assume a target efficiency to estimate input power and input
peak current.
In buck-boost converter, the average of current flow in MOSFET
is equal to the input current. If given a ratio of maximum inductor
current ripple to maximum inductor peak current,
△IL/IL(pk).Then the inductor peak current can be estimated by
the equation:
The maximum inductor current ripple, △is :
From the basic inductor equation, the inductance is :
Follow the equations above, the inductance and maximum
inductor current can be computed. The magnetic design of the
Publication Order Number: [BW7381]
© Bruckewell Technology Corporation Rev. A -2014
BW7381
Universal High Brightness LED Driver
Disclaimer
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NOTICE TO IMPROVE RELIABILITY, FUNCTION OR DESIGN OR OTHERWISE.
Bruckewell Technology Inc., its affiliates, agents, and employees, and all persons acting on its or their behalf
(collectively, “Bruckewell”), disclaim any and all liability for any errors, inaccuracies or incompleteness
contained in any datasheet or in any other disclosure relating to any product.
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Such statements are not binding statements about the suitability of products for a particular application. It is the
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specification is suitable for use in a particular application. Parameters provided in datasheets and/or
specifications may vary in different applications and performance may vary over time.
Product specifications do not expand or otherwise modify Bruckewell’s terms and conditions of purchase,
including but not limited to the warranty expressed therei
Publication Order Number: [BW7381]
© Bruckewell Technology Corporation Rev. A -2014
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