DS8486 00

®
RT8486
Isolated Secondary-Side Lighting LED Controller
General Description
Features
The RT8486 is an isolated secondary-side lighting LED
controller designed specifically for lighting fixtures such
as E27, GU10, T5 and T8. The IC is suitable for applications
that require power line isolation for safety, reliability, high
conversion efficiency, as well as high LED current accuracy.
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Secondary-Side LED Current Regulation
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4.75V to 48V Operating Input Range
High Accuracy LED Current Threshold Control
0.6mA Operating Current
Adjustable LED Current
Output Over-Voltage Protection
Small SOT-23-6 Package
RoHS Compliant and Halogen Free
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The RT8486 contains 1) a constant current regulating
amplifier with 140mV threshold used to program the LED
string current with a simple resistor to within 5% LED
current accuracy; 2) an over-voltage comparator to protect
the output when LED string is open or broken; 3) an optocoupler driver to control the primary-side of the transformer
to complete the system loop.
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Applications
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Isolated LED Lighting Fixtures
E27/GU10/T5/T8
Marking Information
The RT8486 is offered in the small SOT-23-6 package.
06= : Product Code
06=DNN
Ordering Information
DNN : Date Code
RT8486
Package Type
E : SOT-23-6
Pin Configurations
(TOP VIEW)
Lead Plating System
G : Green (Halogen Free and Pb Free)
VCC OUT CP
Note :
6
Richtek products are :
`
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
5
4
2
3
CN GND OVP
Suitable for use in SnPb or Pb-free soldering processes.
SOT-23-6
Simplified Application Circuit
D1
VOUT
Opto-Coupler
VCC
Secondary
side winding
R1
RLED
RT8486
RVC1
CVC1
OUT
CVCC
LED String
OVP
RIC1
GND CP
CN
R2
CIC1
RCN
RSENSE
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8486-00 April 2013
is a registered trademark of Richtek Technology Corporation.
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1
RT8486
Typical Application Circuit & Function Block Diagram
D1
VOUT
Opto-Coupler
VCC
RLED
R1
RT8486
Secondary
side winding
CVCC
LED String
OUT
2.5V
- CV
RVC1 CVC1
+
OVP
140mV
- CC
RIC1
+
R2
CIC1
CP
CN
GND
RCN
RSENSE
Operation
The operation input voltage range is from 4.75V to 48V for
the RT8486. An internal 2.5V reference voltage is generated
from VCC input power for internal bias voltage. The RT8486
is used to clamp the transformer secondary-side output
voltage by the CV control loop and regulate the LED string
current by the CC control loop at the same time.
The transformer secondary-side output voltage can be
monitored by the OVP pin. The sensed OVP pin voltage
is compared with the 2.5V internal reference. When the
OVP pin voltage is higher than 2.5V, the OUT pin starts
to sink more current to allow the external opto-coupler
and controller at primary-side to reduce the power output
to transformer secondary.
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2
The LED string current can be regulated by the CN pin
voltage through the current sense resistor connected
between the CN and CP pins. The CN pin voltage is
compared with the 140mV internal reference. When the
CN pin voltage is greater than 140mV, the OUT pin will
sink more current to adjust the LED current through an
external opto-coupler and controller at primary-side.
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DS8486-00 April 2013
RT8486
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
CN
Non-Inverting Input of the CC Regulating Amp. It has a offset from the CP pin. The CN
pin should be connected to the "Current In" node of the current sensing resistor,
RSENSE.
2
GND
Ground. This pin should be connected to the ground of the secondary-side.
3
OVP
Over-Voltage Protection Sense Input with Threshold of 2.5V.
4
CP
Inverting Input of the CC Regulating Amp. It has a offset from the CN pin. The CP pin
connects to a resistor to set LED current.
5
OUT
Open-Collector Output. Connect this pin to an opto-coupler with a current limiting
resistor.
6
VCC
Supply Voltage Input. A 0.1μF bypass capacitor should be connected between VCC
and GND.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8486-00 April 2013
is a registered trademark of Richtek Technology Corporation.
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3
RT8486
Absolute Maximum Ratings
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(Note 1)
VCC, OUT to GND ---------------------------------------------------------------------------------------------------------CP to GND ------------------------------------------------------------------------------------------------------------------CN to GND -------------------------------------------------------------------------------------------------------------------OVP to GND ----------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOT-23-6 --------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
SOT-23-6, θJA ---------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------------
Recommended Operating Conditions
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−0.3V to 52V
−0.6V to 1V
−0.3V to 1V
−0.3V to 6V
0.48W
208.2°C/W
260°C
150°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Input Voltage, VCC (Note5) --------------------------------------------------------------------------------- 4.75V to 48V
Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VCC = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Quiescent Current
ICC
V CN = VCP = 0V
--
550
--
μA
GND Pin Current
IGND
V CN = VCP = 0V, GND = 0V
--
530
--
μA
OVP Voltage
V OVP
V CN = VCP = 0V
2.46
2.5
2.54
V CN = VCP = 0V, T A = −25°C to 105°C
2.45
--
2.55
OVP Input Bias Current
IOVP
--
--
100
LED Current Sensing
Amplifier Threshold
V CN−CP
V OVP = 2.4V
135
141
147
V OVP = 2.4V, TA = −25°C to 105°C
134
--
149
--
--
200
nA
--
8
--
mA
CN Input Bias Current
OUT Maximum Sink
Current
V OVP = 2.4 to 2.6V
ICN
IOUT
V OUT = 1.5V
V
nA
mV
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and 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 may
affect device reliability.
Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. RT8486 starts regulation at VCC ≥ 4.5V, and meets all parameter specs at VCC ≥ 4.75V.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS8486-00 April 2013
RT8486
Typical Operating Characteristics
VOVP vs. Temperature
ICC vs. Temperature
2.52
680
VCC
VCC
VCC
VCC
640
45V
36V
12V
4.75V
2.51
VCC
VCC
VCC
VCC
2.50
VOVP (V)
I CC (µA)
600
=
=
=
=
560
520
=
=
=
=
45V
36V
12V
4.75V
2.49
2.48
480
2.47
440
2.46
400
-50
-25
0
25
50
75
100
-50
125
-25
0
50
75
100
125
Temperature (°C)
Temperature (°C)
VOUT vs. Temperature
IOVP vs. Temperature
1.0
50
0.9
45
35
30
=
=
=
=
45V
36V
12V
4.75V
0.8
0.7
VOUT (V)
VCC
VCC
VCC
VCC
40
I OVP (nA)
25
25
20
0.5
0.3
10
0.2
5
0.1
0
0.0
-25
0
25
50
75
100
=
=
=
=
45V
36V
12V
4.75V
0.4
15
-50
VCC
VCC
VCC
VCC
0.6
IOUT = 2mA
-50
125
-25
0
25
50
75
100
125
100
125
Temperature (°C)
Temperature (°C)
IOUT vs. Temperature
VCN-CP vs. Temperature
146
10
9
144
8
VCN-CP (mV)
I OUT (mA)
7
6
VCC
VCC
VCC
VCC
5
4
3
=
=
=
=
45V
36V
12V
4.75V
2
142
VCC
VCC
VCC
VCC
140
=
=
=
=
45V
36V
12V
4.75V
138
136
1
134
0
-50
-25
0
25
50
75
100
Temperature (°C)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS8486-00 April 2013
125
-50
-25
0
25
50
75
Temperature (°C)
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5
RT8486
Application Information
Output Voltage Setting
Compensation
The voltage control loop is controlled via the first transconductance operational amplifier. An opto-coupler which
is directly connected to the output and an external resistor
bridge is connected between the output positive line and
the ground reference. The middle point is to be connected
to the OVP pin of the RT8486, where R2 is the upper
resistor and R1 is the lower resistor of the bridge. The
relationship between R2 and R1 is shown as the equation
below :
(R1+ R2 )
VOUT = VOVP ×
R2
( V − VOVP )
R1 = R2 × OUT
VOVP
Both the voltage control transconductance amplifier and
the current control transconductance amplifier can be fully
compensated. The output and negative inputs are directly
accessible for external compensation components, as
shown in the Typical Application Circuit.
where VOUT is the desired maximum output voltage. To
avoid discharge of the load, the resistor bridge R1, R2,
should be highly resistive. For this type of application a
total value of 100kΩ (or more) would be appropriate for
the resistors R1 and R2.
As an example, with R1 = 80kΩ and R2 = 20kΩ,
VOUT = 12.5V.
Output Current Setting
The current control loop is controlled via the second
transconductance operational amplifier. An opto-coupler
and the sense resistor, RSENSE, is placed in series on the
output negative line. VCN−CP threshold is achieved
externally by a resistor bridge tied to the reference voltage,
VREF. Its middle point is tied to the positive input of the
current control operational amplifier and its foot is
connected to the lower potential point of the sense resistor.
The resistors of the bridge are matched to provide the best
precision. With VCN−CP and RSENSE, the expected output
current, IOUT, can be obtained as the equation below :
IOUT
V
= CN−CP
RSENSE
where IOUT is the desired maximum output current, and
VCN−CP is the threshold voltage for the current control loop.
Note that, the sense resistor, RSENSE, should be chosen
taking into account its maximum power dissipation (PLIM)
during full load operation.
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The typical component values for the compensation
network of voltage control loop is CVC1 = 2.2nF and
RVC1 = 22kΩ. The typical component values for the
compensation network of current control loop is
CIC1 = 2.2nF, RIC1 = 22kΩ and RCN = 1kΩ. However, in
many application conditions, the current control loop can
be stable without compensation network (RCN = 0, no
CIC1 nor RIC1).
When the voltage control loop is used as the voltage limit
protection or the current control loop is used as the current
limit protection, no compensation network is needed for
the protecting control loop.
A resister, ROPT, must be connected in series with the
opto-coupler since it is part of the compensation network.
Although the value of ROPT is not critical, it's recommended
to be in the range from 0.33kΩ to (VOUT − 2) / (0.005)Ω.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
SOT-23-6 package, the thermal resistance, θ JA, is
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DS8486-00 April 2013
RT8486
208.2°C/W on a standard JEDEC 51-7 four-layer thermal
test board. The maximum power dissipation at TA = 25°C
can be calculated by the following formula :
PD(MAX) = (125°C − 25°C) / (208.2°C/W) = 0.48W for
SOT-23-6 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 1 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Layout Consideration
For the best performance of the RT8486, the following
PCB Layout guidelines must be strictly followed.
`
Place the RSENSE resistor as close to the IC as possible.
`
Keep the input/output traces as wide and short as
possible.
Secondary
side winding
D1
VOUT
Optocoupler
Maximum Power Dissipation (W)1
0.6
RLED
Four-Layer PCB
R1
0.5
RVC1 CVC1
0.4
CVCC
RIC1
:
: LED String
:
CIC1
0.3
VCC OUT CP
0.2
6
5
4
2
3
GND
0.1
CN GND OVP
0.0
0
25
50
75
100
R2
125
RCN
Ambient Temperature (°C)
Figure 1. Derating Curve of Maximum Power Dissipation
RSENSE
Figure 2. PCB Layout Guide
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is a registered trademark of Richtek Technology Corporation.
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7
RT8486
Outline Dimension
H
D
L
C
B
b
A
A1
e
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
0.889
1.295
0.031
0.051
A1
0.000
0.152
0.000
0.006
B
1.397
1.803
0.055
0.071
b
0.250
0.560
0.010
0.022
C
2.591
2.997
0.102
0.118
D
2.692
3.099
0.106
0.122
e
0.838
1.041
0.033
0.041
H
0.080
0.254
0.003
0.010
L
0.300
0.610
0.012
0.024
SOT-23-6 Surface Mount Package
Richtek Technology Corporation
5F, No. 20, Taiyuen Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot
assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be
accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
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DS8486-00 April 2013
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