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OCP8155
„ Description
OCP8155 is a high precision constant current LED
driver IC with an integrating 650V power MOSFET,
designed for offline flyback constant current LED
lighting within 18W output power, and suitable for
universal input voltage from 85VAC to 265VAC.
IC adopts DIP-8L package. OCP8155 utilizes
primary-side feedback technology to achieve excellent
line regulation and load regulation without TL431,
optical coupling and feedback circuit, greatly saving the
system cost and size.
OCP8155 is provided with perfect protection
functions. The chip detects the VCC pin for
over-voltage detection, and once detecting an
over-voltage signal, the chip enters a “Hiccups” mode
to limit output power. Meanwhile the chip also includes
LED open/short circuit protection, FB short circuit
protection, under-voltage lockout and over-temperature
protection functions to guarantee the entire system
work safely and stably in harsh working environment.
High Precision Primary-side Feedback
Constant Current Converter
„ Feature
z Internal 650V Power MOSFET
z Primary-side Feedback Technology,
No Secondary-side Feedback Circuit Required
z No Loop Compensation
z ±3% Constant Current Accuracy
z 85VAC~265VAC Universal Input Voltage
z LED Open/Short Circuit Protection
z FB to GND Short Circuit Protection
z Over-temperature Protection
z Under-voltage Lockout Function
z CS Resistance Open Circuit Protection
z Operating Temperature RangeTA=-40 ~ 85
z Available in DIP-8L Package
„ Application
z LED Fluorescent Lamp
z E27Par LampDown Light
z LED BulbSpot Light
z Other LED Lighting
„ Typical Application
Figure 1, Typical Application for OCP8155
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„ Pin Configuration
DIP-8L
OCP8155
„ Pin Definition
Name
CS
CS
FB
VCC
GND
GND
SW
SW
Pin No.
DIP-8L
1
2
3
4
5
6
7
8
Description
Primary-side Output Current Pin.
Current Sense Input Pin.
Connect the feedback dividing resistors and auxiliary
winding to detect output voltage.
Power Supply Pin. Connect a bypass capacitance nearly.
Signal Ground
Signal Ground
Switch Node
Switch Node
„ Electrical Block Diagram
Figure 2, OCP8155 Internal Block Diagram
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OCP8155
„ Absolute Maximum Ratings1
Symbol
Parameters
Range
Units
VCC
VCC pin input voltage
-0.3~25
V
SW Switch node voltage
-0.3~650
V
CS CS current sampling voltage
-0.3~7
V
FB Feedback voltage
-0.3~7
V
θJA
PDMAX2
TJ
TSTO
Thermal resistance
DIP-8L
Power dissipation
Operating junction temperature
Storage temperature range
90
0.45
40 ~ 150
55 ~ 150
°C/W
W
°C
°C
Note1: Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device.
2:The maximum power dissipation decreases if temperature rises, it is decided by TJMAX, θJA, and environment temperature
(TA). The maximum power dissipation is the lower one between PDMAX = (TJMAX - TA)/ θJA and the number listed in the maximum
table.
„ Recommended Operation Conditions
Symbol
parameters
Range
Units
VCC
Power supply voltage
8.0~17.5
V
POUTMAX
Maximum output 85~265VAC
power
220VAC ±15%
18
21
W
TA Operating environment temperature 40 ~ 85
°C
„ Electrical Parameters
(Test condition: Unless other specified, TA =25, VCC=12V)
Symbol
Parameters
Conditions
Supply Voltage Section
VCC_TH
VUVLO
VOVP
VCC_CLAMP
VCC Turn On Voltage Threshold
Under-voltage Lockout Threshold
VCC Over-voltage Protection Threshold
VCC Clamp Voltage Threshold
VCC Rising
Current Sense Section
VCS_TH
Current Sense Threshold
TONMIN
Minimum On Time
Operating Current Section
IST VCC Start-up Current
IOP Typical Operating Current
Feedback section
VCC=6.5V
FOP=40KHz
TDEMAG_Min
Minimum demagnetization time
VFB FB reference voltage
TOFFDLY
Turn-off delay
RLNC
Bulk voltage compensation resistance
Maximum Duty Cycle
DMAX
T
System Maximum Duty Cycle
System Operating Cycle
FSHORT
Short Circuit Operating Frequency
Over-temperature Protection Section
TSD
TSD_HYS
Thermal Shutdown Temperature
Over-temperature Protection Hysteresis
Drive section
RDS(ON)
BVDSS
IDSS
NMOS Drain-Source On-Resistance
Drain-Source Breakdown Voltage
Power MOSFET Drain leakage current
VGS=10V, ID=1A
VGS=0V, ID=250uA
VDS=520V, VGS=0V
Min
12.0
6.4
17.5
21.0
0.99
-
-
-
-
-
-
-
-
-
-
-
-
-
650
-
Typ
14.0
7.2
19
23
1.00
600
32
0.7
3
1
136
900
-
3*Td
7.0
150
50
2.1
-
-
Max Units
16.0 V
8.0 V
20.5 V
25.0 V
1.01
-
V
nS
60 uA
- mA
- uS
-V
- nS
- uV/uA
58 %
-
- kHz
-
-
2.6
-V
2 uA
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OCP8155
„ Typical Parameter Characteristic
VCC_TH vs. Temperature
VOVP vs. Temperature
18
17
16
15
14
13
12
11
10
9
8
-40 -10 20 50 80 110
Temperature()
Output Current vs. Input Voltage
140
20
19.75
19.5
19.25
19
18.75
18.5
18.25
18
17.75
17.5
-40 -10 20 50 80 110
Temperature()
CS Threshold Voltage vs. VCC
140
2
1.6
1.2
0.8
0.4
0
-0.4
-0.8
-1.2
-1.6
-2
85
115 145 175 205 235 265
VAC(V)
Electrical waveforms in the start-up state system
(CH1=CS, CH2=VBULK, CH4=IOUT)
1.1
1.08
1.06
1.04
1.02
1
0.98
0.96
0.94
0.92
0.9
9
10 11 12 13 14 15 16
VCC(V)
Electrical waveforms in the power-off state system
(CH1=CS, CH2=VBULK, CH4=IOUT)
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OCP8155
„ Application Information
OCP8155 is a high precision constant current LED driver IC designed for offline flyback , specially applying to
constant current LED lighting within 18W output power. OCP8155 utilizes primary-side feedback technology to
achieve excellent line regulation and load regulation without TL431, optical coupling and feedback circuit, greatly
saving the system cost and size.
Start Up
OCP8155 only requires 32uA start-up current, than which VCC will rise as long as the current flowing through the
start-up resistor RST is higher. The chip starts up when VCC goes up to 14V (Typical). At this time the operating
current is usually higher than the current provided by the start-up resistor, which leads to VCC decrease. The start-up
process will proceed successfully so long as the auxiliary winding can provide normal power supply to the chip before
VCC deceases below under-voltage lockout threshold.
Turns Ratio Setting
Only when the chip operates in a current discontinuous conduction mode can it keep LED current constant.
When designing the system, the chip operating in a current discontinuous conduction mode should be ensured. In
another word, the designed maximum duty cycle must be less than the inherent maximum duty cycle (58%) in the
chip. Turns Ratio is limited by two factors: the inherent maximum duty cycle and power MOSFET breakdown voltage.
First, turns ratio is considered according to the maximum duty cycle. Then duty cycle is calculated on the basis of
continuous conduction mode:
D = VOR
VBULK + VOR
(1)
According to formula (1), the maximum duty cycle working situation happens to the system when the VBULK is
lowest. Maximum VOR which is limited by maximum duty cycle is gained when duty cycle is set to 58%.
Secondly, turns ratio is considered according to the power MOSFET breakdown voltage.
The Drain-Source breakdown voltage of the power MOSFET is:
VDS = VBULK + VRCD = VBULK + k *VOR < VBK
(2)
Where, VBK is the Drain-Source breakdown voltage of the power MOSFET. The k coefficient affects the leakage
inductance dissipation. Ultra-low value of k leads to large leakage inductance dissipation and low efficiency, while
ultra-high value of k results in requiring high Drain-Source breakdown voltage of the power, so that k is usually set to
1.4~2.
According to formula (2), the power MOSFET endures the largest Drain-Source voltage when VBULK is largest.
Maximum VOR which is limited by breakdown voltage is gained according to the Drain-Source breakdown voltage of
the power MOSFET.
By considering these two aspects above, the lower VOR is selected.
Then turns ratio of primary side and secondary side is calculated according to the following formula:
n p = VOR
ns VO
(3)
According to the chip operating input voltage VCC and output voltage, the turns ratio of auxiliary-side and
secondary-side is calculated by the following formula:
VCC
=
na
ns
*VO
(4)
Constant Current Control
IC compares CS pin voltage with internal 1V threshold voltage to set the primary-side peak current Ipkp of the
transformer:
I pkp
=
1
RCS
(5)
The LED output current IO is gained according to the following formula:
Io
=
1 * np
6 ns
* I pkp
(6)
Where, Ipkp is the primary-side peak current of the transformer, np is the number of the primary-side turns of the
transformer, and ns is the number of the secondary-side turns of the transformer.
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