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PDF RT8456 Data sheet ( Hoja de datos )
| Número de pieza | RT8456 | |
| Descripción | Isolated Secondary Side LED Lighting Current Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT8456
Isolated Secondary Side LED Lighting Current Controller
General Description
The RT8456 is an isolated secondary LED current 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 and reliability, high
conversion efficiency, as well as high LED current accuracy.
The RT8456 contains 1) a constant current regulating
amplifier with 59mV 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) and an
opto-coupler driver to control the primary side of the
transformer to complete the system loop.
The RT8456 is offered in a small SOT-23-6 package.
Ordering Information
RT8456
Package Type
E : SOT-23-6
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Features
z Secondary Side LED Current Regulation
z 4.75V to 48V Operation Range
z High Accuracy 59mV LED Current Threshold Control
z 0.6mA Operating Current
z Programmable LED Current
z Output Over Voltage Protection
z Small SOT-23-6 Package
z RoHS Compliant and Halogen Free
Applications
z Isolated LED Lighting Fixtures
z E27/GU10/T5/T8
Pin Configurations
(TOP VIEW)
VCC OUT CP
654
23
CN GND OVP
SOT-23-6
Marking Information
EM=DNN
EM= : Product Code
DNN : Date Code
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS8456-05 April 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
Application Information
Output Voltage Setting
The voltage control loop is controlled via the first trans-
conductance operational amplifier. An optocoupler 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 RT8456, where R2 is the upper
resistor and R1 the lower resistor of the bridge. The
relationship between R2 and R1 is shown below
(R1 + R2)
VOUT = VOVP x
R2
R1 = R2 x ( VOUT - VOVP )
VOVP
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 optocoupler 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 below equation :
IOUT
=
VCN−CP
RSENSE
where IOUT is the desired maximum output current, and
VCN−CP 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.
RT8456
Compensation
Both the voltage control trans conductance amplifier and
the current control trans-conductance amplifier can be fully
compensated. The output and negative inputs are directly
accessible for external compensation components, as
shown in the Typical Application Circuit.
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.
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS8456-05 April 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
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| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet RT8456.PDF ] | |
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