Applications Note: SY5018B
Single Stage Flyback and PFC Controller
with CV Control
Advanced Design Specification
General Description
SY5018B is a single stage Flyback and PFC controller
targeting at Constant Voltage (CV) applications. Primary
side control is applied to reduce the feedback circuit cost.
It drives the Flyback converter in the Quasi-Resonant
mode for high efficiency and achieves high power factor
by constant on time control scheme. Adaptive
PWM/PFM control is adopted for highest average
efficiency.
Features
•
Primary side CV control eliminates the opto-coupler.
•
Valley turn-on of the primary MOSFET to achieve
low switching losses
•
Internal high current MOSFET driver: 0.1A sourcing
and 0.5A sinking
•
Power factor >0.90 with single-stage conversion
•
Maximum switching frequency limitation 100kHz
•
Compact package: SO8
•
Output current limit, about 1.2 times the rated current
Ordering Information
SY5018
□
(
□□
)
□
Temperature Code
Package Code
Optional Spec Code
Ordering Number
SY5018BFAC
Package type
SO8
Note
----
Applications
•
AC/DC adapters
•
Battery Chargers
•
LED Lighting
Typical Applications
Efficiency vs. Input Voltage (V
AC
)
93
92
91
90
89
88
80
110
140
170
200
230
260
290
Input Voltage (V
AC
)
Figure 1. Schematic Diagram
AN_SY5018B Rev.0.0
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AN_SY5018B
Pinout
(
top view)
(SO8)
Top Mark: BEV
xyz
(device
code: BEV,
x=year code, y=week code, z= lot number code)
Pin
1
2
3
4
5
6
7
Name
COMP
CLIM
ISEN
GND
DRV
VIN
VSEN
Description
Loop compensation pin. Connect a RC network across this pin and ground to stabilize the control loop.
Add 220nF ceramic capacitor to GND, output current will be limited to about 1.2 times the rated current.
If do not need this function, connect CLIM PIN to GND.
Current limit PIN.
Ground pin.
Gate driver pin. Connect this pin to the gate of primary MOSFET with a resistor.
Power supply pin.
Output voltage and inductor current zero detection PIN. This pin receives the auxiliary winding voltage
by a resistor divider.
Block Diagram
f
_LIMIT
Control
o
l
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AN_SY5018B
Absolute Maximum Ratings
(Note 1)
VIN, DRV -----------------------------------------------------------------------------------------------------------------
Supply current I
VIN
----------------------------------------------------------------------------------------------------------------
VSEN ----------------------------------------------------------------------------------------------------------------
ISEN, COMP, CLIM---------------------------------------------------------------------------------------------------------------
Power Dissipation, @ T
A
= 25°C SO8 -----------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
SO8,θ
JA
---------------------------------------------------------------------------------------------------------------
SO8,θ
JC
---------------------------------------------------------------------------------------------------------------
Temperature Range ---------------------------------------------------------------------------------------------------
Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------------------------------------
Storage Temperature Range -----------------------------------------------------------------------------------------
-0.3V to 36V
20mA
-0.3V to V
IN
+0.3V
3.6V
1.1W
88°C/W
45°C/W
-
40°C to 150°C
260°C
-
65°C to 150°C
Recommended Operating Conditions
(Note 3)
VIN, DRV ----------------------------------------------------------------------------------------------------------------------
Absolute maximum range---------------------------------------------------------------------------------------------
9V~22V
-40°C to 150°C
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AN_SY5018B
Electrical Characteristics
(V
IN
= 12V (Note 3), T
A
= 25°C unless otherwise specified)
Parameter
Symbol
Test Conditions
Power Supply Section
Input voltage range
VIN turn-on threshold
VIN turn-off threshold
VIN OVP voltage
Start up Current
Operating Current
Shunt current in OVP mode
Error Amplifier Section
Current limit Voltage
Maximum Current Voltage
V
FB
at fast start up
Internal reference voltage
Threshold value of Max V
FB
OVP voltage threshold
Blanking time for OFF time
Gate driver voltage
Typical source current
Typical sink current
Max ON Time
Min ON Time
Maximum switching frequency
Output current limit
Thermal Section
Thermal Shutdown Temperature
Min
9
21.5
7.5
24.5
5
1
2.5
0.4
1.0
1.5
1.0
1.25
1.40
1.50
1.7
2.6
12
100
500
Typ
Max
22
Unit
V
V
V
V
µA
mA
mA
V
V
V
V
V
V
V
µs
µs
V
mA
mA
µs
µs
kHz
V
℃
V
V
VIN
V
V
I
I
VIN_ON
VIN_OFF
VIN_OVP
ST
VIN
V
VIN
<V
VIN_OFF
I
C
L
=100pF,f=15kHz
VIN_OVP
V
VIN
>V
VIN_OVP
V
V
V
V
V
t
t
V
ISEN_LIMIT
ISEN_EX
VSEN<0.2V
1.0V>VSEN>0.2V
FB_LOW
REFV
FB_HIGH
V
VSEN_OVP
V
V
ISEN_HOLD
ISEN_HOLD
=0.15V
=0.40V
OFF_MIN1
OFF_MIN2
Gate
I
I
SOURCE
t
t
SINK
ON_MAX
Vcomp=2.5V
10
0.4
100
0.33
150
f
ON_MIN
V
T
MAX
CLIM
SD
Note 1:
Stresses beyond the “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress
ratings only. Functional operation of the device at these or any other conditions beyond those indicated in the operational
sections of the specification is not implied. Exposure to absolute maximum rating conditions for extended periods may
affect device reliability.
Note 2:
θ
JA
is measured in the natural convection at T
A
= 25°C on a low effective single layer thermal conductivity test
board of JEDEC 51-3 thermal measurement standard. Test condition: Device mounted on 2” x 2” FR-4 substrate PCB, 2oz
copper, with minimum recommended pad on top layer and thermal vias to bottom layer ground plane.
Note 3:
Increase VIN pin voltage gradually higher than V
VIN,ON
voltage then turn down to 12V.
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AN_SY5018B
Operation
SY5018B is a constant voltage Flyback controller with
primary side control and PFC function that targets at LED
lighting applications.
The Device provides primary side control to eliminate the
opto-couplers or the secondary feedback circuits, which
would cut down the cost of the system.
High power factor is achieved by constant on operation
mode, with which the control scheme and the circuit
structure are both simple.
Start up process is optimized inside SY5018B, and quick
start up (less than 500ms) is achieved without any
additional circuit
In order to reduce the switching losses and improve EMI
performance, Quasi-Resonant switching mode is applied,
which means to turn on the power MOSFET at voltage
valley; The start up current of SY5018B is rather small
(5µA typically) to reduce the standby power loss further.
The maximum switching frequency is clamped to 100kHz
to reduce switching losses and improve EMI performance;
Specific design is adopted to ensure good performance
when transition.
Adaptive PWM/PFM control is adopted for highest
average efficiency.
SY5018B provides reliable protections such as Short
Circuit Protection (SCP), Open LED Protection (OLP),
Over Temperature Protection (OTP), transformer shorted
protection and power diode shorted protection, etc.
SY5018B is available with SO8 package.
Fig3. Start up
This operation is aimed to build up enough output voltage for
auxiliary winding bias supply as quickly as possible. It is enabled
only one time just when V
VIN
is over V
VIN,ON
.
V
V
FB,LOW
, V
COMP
is under charge of the internal gain
modulator.
is pre-charged by internal current source to
V
COMP,IC
and hold at this level until fast start up process
is finished.
COMP
The start up resistor R
ST
and C
VIN
are designed by rules
below:
(a)
Preset start-up resistor R
ST
, make sure that the current
through R
ST
is larger than I
ST
and smaller than I
VIN
_
OVP
V
V
I
BUS
BUS
I
VIN_OVP
<R
ST
<
Applications Information
Start up
After AC supply or DC BUS is powered on, the capacitor
C
VIN
across VIN and GND pin is charged up by BUS
voltage through a start up resistor R
ST
. Once V
VIN
rises up
to V
VIN,ON
, the internal blocks start to work and PWM
output is enabled.
The output voltage is feedback by VSEN pin, which is
taken as V
FB
. If V
FB
is lower than certain threshold
V
FB,LOW
, which means the output voltage is not built up,
V
COMP
is pulled up to high clamped; if V
FB
is higher than
ST
Where V
BUS
is the BUS line voltage.
(b)
Select C
VIN
to obtain an ideal start up time t
ST,
and
ensure the output voltage is built up at one time.
(
C
VIN
=
V
BUS
V
R
ST
-I
ST
)× t
ST
VIN_ON
(d)
If the C
VIN
is not big enough to build up the output
voltage at one time. Increase C
VIN
and decrease R
ST
, go
back to step (a) and redo such design flow until the ideal
start up procedure is obtained.
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