Application Notes: AN_SY5839
Single Stage Buck PFC Controller
For LED Lighting
Preliminary datasheet
General Description
The SY5839 is a single stage Buck PFC controller
targeting at LED lighting applications. It is a primary side
controller without applying any secondary feedback
circuit for low cost, and drives the Flyback converter in
the quasi-resonant mode to achieve higher efficiency. It
keeps the Flyback converter in constant on time operation
to achieve high power factor. It adopts special design to
achieve quick start up and reliable protection for safety
requirement.
Features
•
•
•
•
•
•
•
Valley turn-on of the MOSFET to achieve low
switching losses
Power factor >0.90 with single-stage conversion.
Low start up current: 15
µ
A typical
Quick start up <500ms
Reliable short LED and Open LED protection
Power factor >0.90 with single-stage conversion.
Compact package: SOT23-6
Ordering Information
SY5839
□(□□)□
Tempera ture Code
Packa ge Code
Optional Spec Code
Ordering Number
SY5839ABC
Package type
SOT23-6
Note
----
Applications
•
•
•
•
•
LED lighting
Down light
Tube lamp
PAR lamp
Bulb l mp
Typical Applications
Efficiency vs. Input Voltage (V
AC
)
93
Efficiency (%)
92
91
I
O
=225mA
P
O
=18W
90
170
190
210
230
250
270
Input Voltage (V)
Figure 1. Schematic Diagram
Figure 2. Efficiency vs Input Voltage
AN_SY5839 Rev. 0.1
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AN_SY5839
Pinout
(
top view)
(SOT-23)
Top Mark: ZTxyz (device
code:
ZT,
x=year code, y=week code, z= lot number code)
Pin Name
Pin Number
Pin Description
Current sense pin. Connect this pin to the source of the switch. Connect
the sense resistor across the source of the switch and the GND pin.
(current sense resister R
S
:
I
ISEN
1
=
1
×
V
REF
) .Also this pin used to detect
o
2
R
S
GND
COMP
2
3
VSEN
4
VIN
DRV
5
6
transformer and secondary is short or not.
Ground pin
Loop compensation pin. Connect a RC network across this pin and
ground to stabilize the cont ol loop.
Inductor current zero-crossing detection pin. This pin receives the
auxiliary winding vo tage by a resister divider and detects the inductor
current zero crossing point. This pin also provides over voltage
protection and l ne regulation modification function simultaneously. If
the voltage on this pin is above V
SEN,OVP
, the IC would enter over
voltage prot ction mode. Good line regulation can be achieved by
adjust ng the upper resistor of the divider.
Power supply pin. This pin also provides output over voltage protection
alo g with VSEN pin.
Gate drive pin. Connect this pin to the gate of MOSFET.
AN_SY5839 Rev. 0.1
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AN_SY5839
Absolute Maximum Ratings
(Note 1)
VIN, DRV -------------------------------------------------------------------------------------------------------------------
Supply Current I
VIN
--------------------------------------------------------------------------------------------------------------
VSEN-------------------------------------------------------------------------------------------------------------------
ISEN, COMP ----------------------------------------------------------------------------------------------------------------
Power Dissipation, @ T
A
= 25°C SOT23-6 ------------------------------------ ------------------------------------------------
Package Thermal Resistance (Note 2)
SOT23-6,
θ
JA
-------------------------------------------------------------------------------------------------------
SOT23-6,
θ
JC
-------------------------------------------------------------------------------------------------------
Junction Temperature Range ----------------------------------------------------------------------------------------
Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------------------------------------
Storage Temperature Range -----------------------------------------------------------------------------------------
0.3V~33V
15mA
-0.3V ~V
IN
+0.3
0.3~3.6V
0.6W
-
-
170°C/W
130°C/W
-
40°C to 150°C
260°C
-
65°C to 150°C
Recommended Operating Conditions
(Note 3)
VIN, DRV --------------------------------------------------------------------------------------------------------------------
Junction Temperature Range ----------------------------------------------------------------------------------------
9.5V~27V
-40°C to 125°C
Block Diagram
Figure3. Block Diagram
AN_SY5839 Rev. 0.1
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AN_SY5839
Electrical Characteristics
(V
IN
= 12V (Note 3), T
A
= 25°C unless otherwise specified)
Parameter
Power Supply Section
VIN turn-on threshold
VIN turn-off threshold
VIN OVP voltage
Start up Current
Shunt current in OVP mode
Error Amplifier Section
Internal reference voltage
Current Sense Section
Current limit voltage
Protection limit for TR short
CC Feedforward coefficient
CC Feedforward resistor
COMP section
Pre-charge value
VSEN pin Section
VSEN pin OVP voltage
threshold
Fast start up theshold
Gate Driver Section
Gate driver voltage
Maximum source current
Minimum sink current
Max ON Time
Max OFF Time
Blanking time for ON time
Blanking time for OFF time
Maximum switching frequency
Thermal Section
Thermal Shutdown
Temperature
Symbol
V
VIN,ON
V
V
I
I
Test Conditions
Min
Typ
25.3
8.5
30.0
15
4.7
0.3
0.75
1.5
0.1
340
1.4
Max
Unit
V
V
V
µA
mA
V
V
V
Ω
V
VIN,OFF
VIN,OVP
ST
V
V
VIN
<V
VIN,OVP
VIN
>V
VIN,OFF
VIN,OVP
V
V
REF
V
ISEN,LIMIT
ISEN,EX
K
R
V
2
K2
COMP,LIM
V
VSEN,OVP
V
1.5
0.55
11.7
0.06
0.25
20
150
350
2
113
V
V
V
A
A
µs
µs
VSEN,ST
V
I
Gate
SOURCE
I
T
T
SINK
ON,MAX
T
T
OFF,MAX
ON,BLK
ISEN=0V
VFB<0.55V
ns
µs
OFF,BLK
f
MAX
kHz
T
SD
150
C
Note 1:
Stresses beyond the “Absolute Maximum Ratings” ma y cause permanent damage to the device. These are stress
ratings only. Functi nal 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:
ſ
JA
is measured in the natural convection at T
A
= 25°C on a low effective single layer thermal con ductivity
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.
AN_SY5839 Rev. 0.1
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AN_SY5839
Operation
SY5839 is a constant current Buck PFC controller
targeting at LED lighting applications.
High power factor is achieved by constant on-time
operation mode, with which the control scheme and the
circuit structure are both simple.
Start up process is optimized inside SY5839, 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 SY5839 is rather small (15µA
typically) to reduce the standby power loss further; the
maximum switching frequency is clamped to 125kHz to
reduce switching losses and improve EMI performance
when the converter is operated at light load condition.
SY5839 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.
.
SY5839 is available with SOT23-6
V
VIN
V
VIN,ON
V
VIN,OFF
t
High
clamped
V
COMP,IC
V
COMP,INT
V
COMP
t
PWM
V
FBV
t
V
FB,ST
t
Fig. Start up
This operation is aimed to build up enough output voltage
for auxilia y winding bias supply as quickly as possible. It
is enabled only one time just when V
VIN
is over V
VIN,ON
.
V
COMP
is pre-charged by internal current source to
V
COMP,IC
and hold at this level until fast start up process
is finished.
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
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
FBV
is lower than certain threshold
V
VSEN,ST
, which means the output voltage is not built up,
V
COMP
is pulled up to high clamped; if V
FBV
is higher
than V
V EN,ST
, V
COMP
is under charge of the internal gain
modulator.
V
BUS
V
BUS
I
VIN_OVP
<R
ST
<
I
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.
V
BUS
-I
ST
)
×
t
ST
(
C
R
ST
VIN
=
V
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.
AN_SY5839 Rev. 0.1
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