RT8417
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
DS8417-00 August 2017 www.richtek.com 1
Buck LED Driver Controller with Active PFC and HV Start-up Device
General Description
The RT8417 is a floating buck constant current LED
driver with active power factor correction (PFC). It
supports high power factor across a wide range of line
voltages, and it drives the converter in the boundary
conduction mode (BCM) to achieve higher efficiency
and better EMI performance.
A high voltage (HV) start-up device is integrated in the
RT8417 to shorten the start-up time and reduce the
external component count, the cost, and the volume of
the driver board.
This driver can use a cheap simple drum core inductor
in the system instead of an EE core. In addition, the
current through the inductor is sensed directly and
excellent current regulation is provided.
The RT8417 embeds comprehensive protection
functions for robust designs, including LED open-circuit
protection, LED short-circuit protection, VCC
Under-Voltage Lockout (UVLO), VCC Over-Voltage
Protection (VCC OVP), Over-Temperature Protection
(OTP), and cycle-by-cycle current limitation.
Ordering Information RT8417
Package Type
S : SOP-8
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
RoHS compliant and compatible with the current
requirements of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes
Marking Information
RT8417
GSYMDNN
RT8417GS : Product Number
YMDNN : Date Code
Features Excellent LED Current Regulation
Fast Start-up
Power Factor Correction
Low System BOM Cost
Boundary Conduction Mode (BCM)
Extremely Low Operating Current
Multiple Protection Features :
LED Open-Circuit Protection
LED Short-Circuit Protection
VCC Under-Voltage Lockout
VCC Over-Voltage Protection
Over-Temperature Protection
Cycle-by-Cycle Current Limit
Applications E27, PAR, Light Bar, Offline LED Lights
Pin Configuration
(TOP VIEW)
DMG
VC
GND
VCC
HV
NC
SENSE
GATE
2
3
4 5
6
7
8
SOP-8
RT8417
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Functional Pin Description
Pin No. Pin Name Pin Function
1 DMG Feedback voltage detection input. This pin detects the output voltage.
2 VC Compensation node. Output of the internal trans-conductance amplifier.
3 GND Ground of the controller.
4 VCC
Supply voltage input. The controller will be enabled when VCC exceeds
VUVLO_ON (8.5V typ.) and disabled when VCC decreases lower than
VUVLO_OFF (7V typ.).
5 SENSE Current sense input. The typical sensing threshold is 200mV between the
SENSE and GND pin.
6 GATE Gate driver output for External MOSFET switch.
7 NC No internal connection.
8 HV High voltage input for supply voltage.
Functional Block Diagram
GATE
Regulator
GND
SENSE State
Machine
VCC
VC
Gate Driver
JFET
Control
HV
DMG
Current
Sense
EA+
-
Operation The RT8417 senses true average output current and
keeps the system driving constant output current. The
VC pin is the compensation node in this close loop
system and dominates the frequency response. To
stabilize the system and achieve better PFC/ THD,
proper selection of a compensation network is needed.
RT8417
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
DS8417-00 August 2017 www.richtek.com 3
Absolute Maximum Ratings (Note 1)
Supply Input Voltage ------------------------------------------------------------------------------------------------ 0.3V to 40V
Power Dissipation, PD @ TA = 25C
SOP-8 ------------------------------------------------------------------------------------------------------------------- 0.53W
Package Thermal Resistance (Note 2)
SOP-8, JA ------------------------------------------------------------------------------------------------------------- 188C/W
SOP-8, JC ------------------------------------------------------------------------------------------------------------- 47C/W
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------- 260C
Junction Temperature ----------------------------------------------------------------------------------------------- 150C
Storage Temperature Range -------------------------------------------------------------------------------------- 65C to 150C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions (Note 4)
Supply Input Voltage ------------------------------------------------------------------------------------------------ 10V to 30V
Ambient Temperature Range-------------------------------------------------------------------------------------- 40C to 85C
Junction Temperature Range ------------------------------------------------------------------------------------- 40C to 125C
Electrical Characteristics (VCC = 24V, TA = 25C, unless otherwise specified)
Parameter Symbol Test Conditions Min Typ Max Unit
JEFT Supply Current IJFET 4.2 5.7 7.2 mA
JFET Turn off Level VJFET_H 11 12 13 V
JFET Turn on Level VJFET_L 10 11 12 V
JFET Leakage -- -- 50 A
VCC UVLO ON VUVLO_ON 7.5 8.5 9.5 V
VCC UVLO OFF VUVLO_OFF 6 7 8 V
VCC Shut Down Current ISHDN VCC = 15V -- -- 20 A
VCC Quiescent Current IQ Gate stands still 162 270 378 A
VCC OVP Level VOVP 34 37 39.5 V
Internal Reference Voltage VSENSE 194 200 206 mV
SENSE Peak Voltage
Limitation VCL 1.19 1.33 1.47 V
GATE Clamp Level VGATE_H 0mA 10.5 12.5 15 V
10mA 9 12 15 V
GATE Driver Rising Time tR CGATE = 1nF -- 80 --
ns Falling Time tF CGATE = 1nF -- 30 --
DMG High Protection Level VDMG_H 1.48 1.58 1.67 V
RT8417
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
www.richtek.com DS8417-00 August 2017 4
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. JA is measured under natural convection (still air) at TA = 25C with the component mounted on a high
effective-thermal-conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard. JC is measured
at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution recommended.
Note 4. The device is not guaranteed to function outside its operating conditions
RT8417
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
DS8417-00 August 2017 www.richtek.com 5
Typical Application Circuit
DMG
VC
GND
VCC
HV
NC
GATE
SENSE
RT8417
1 8
7
6
54
3
2
DMG
CVCC
4.7μF
CVC
0.22μF
Bridge Rectifier
RHV
10k
RSENSE
RDMG1
RDMG2CDMG
47pF
DMG
CIN
L
Q1
COUT
RG
Line
Neutral
D1
RT8417
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
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Typical Operating Characteristics
VUVLO_ON vs. Temperature
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
-50 -25 0 25 50 75 100 125
Temperature (°C)
VU
VL
O_
ON (
V)
VUVLO_OFF vs. Temperature
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
-50 -25 0 25 50 75 100 125
Temperature (°C)
VU
VL
O_
OF
F (
V)
VCC OVP vs. Temperature
32
33
34
35
36
37
38
-50 -30 -10 10 30 50 70 90 110 130 150 170
Temperature (°C)
VC
C O
VP
(V
)
VSENSE vs. Supply Voltage
195
196
197
198
199
200
201
202
203
204
205
5 10 15 20 25 30 35
Supply Voltage (V)
VS
EN
SE (
mV
)
VSENSE vs. Temperature
150
160
170
180
190
200
210
220
230
240
250
-50 -25 0 25 50 75 100 125
Temperature (°C)
VS
EN
SE (
mV
)
VDMG_H vs. Supply Voltage
1.30
1.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.75
1.80
5 8 11 14 17 20 23 26 29 32 35
Supply Voltage (V)
VD
MG
_H (V
)
RT8417
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DS8417-00 August 2017 www.richtek.com 7
VDMG_H vs. Temperature
1.30
1.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.75
1.80
-50 -25 0 25 50 75 100 125
Temperature (°C)
VD
MG
_H (
V)
RT8417
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
www.richtek.com DS8417-00 August 2017 8
Application Information
The RT8417 is a boundary conduction mode (BCM),
high efficiency constant current controller with internal
high side driver, which can be used in floating buck
configuration, to provide a constant output current to
the LED load. It contains special circuitry for achieving
high power factor (PF) and low input current total
harmonic distortion (THD). A high voltage (HV) start-up
device is integrated in the RT8417 to shorten the
start-up time and reduce the external component count,
the cost, and the volume of the driver board.
The RT8417 provides excellent current regulation by
the average current feedback loop control. The internal
reference voltage (200mV typ.) is used to set the
average output current. The average current is set by
the external resistor, RSENSE. The sense voltage is
also used for over current protection (OCP) function.
The typical OCP threshold is about seven times of the
sense voltage threshold.
Under Voltage Lockout (UVLO)
The RT8417 includes a UVLO function with 1.5V
hysteresis. For system start up, the VCC must rise over
8.5V (typ.) to turn on the GATE terminal. The GATE
terminal will turn off if VCC falls below 7V (typ.)
Setting Average Output Current
The output current that flows through the LED string is
set by an external resistor, RSENSE, which is connected
between the GND and SENSE pins. The relationship
between output current, IOUT, and RSENSE is shown
below :
IOUT = 200mV (typ.)
RSENSE (mA)
Output Over-Voltage Protection
The RT8417 DMG pin provides the Over-Voltage
Protection (OVP) function. When the MOSFET is
turned off, the DMG pin detects the output voltage.
When the DMG pin voltage exceeds DMG OVP
threshold (VDMG_H, 1.58V typ.), DMG OVP will be
activated and the GATE pin will be forced low to turn off
the main switch.
The output OVP level VOVP is set by the resistor divider
RDMG1 and RDMG2 :
VOVP = (1+RDMG1
RDMG2
) ×1.58 (typ.) (V)
It is recommended set VOVP at 120% of nominal output
voltage and set RDMG2 = 2k to 5k.
When the MOSFET is turned off, the resonance
voltage on DMG pin may make the controller false
trigger the DMG OVP. It is recommended to add a
10pF to 47pF bypass capacitor, and it should be as
close to DMG pin as possible.
Input Diode Bridge Rectifier Selection
The current rating of the input bridge rectifier is
dependent on the VOUT / VIN conversion ratio and out
LED current. The voltage rating of the input bridge
rectifier, VBR, is only dependent on the input voltage.
Thus, the VBR rating is calculated as below :
VBR = 1.2 2 VAC MAX
where VAC, Max is the maximum input voltage (RMS)
and the parameter 1.2 is used for safety margin.
For this example :
VBR = 1.2 2 VAC MAX = 1.2 2 264 = 448V
If the input source is universal, VBR will reach 448V.
Input Capacitor Selection
The voltage rating of the input filter capacitor CIN
should be large enough to handle the input voltage.
INC 1.2 2 VAC MAX = 1.2 2 264 = 448V
Inductor Selection
For high PF application, the RT8417 operates the
converter in BCM. The inductance range is defined by
peak current of inductor, maximum and minimum value
of switching on time and off time, for ensuring the
inductor operates in BCM. The peak current of inductor
is showed as belowb :
IPEAK = 2PIN
VPEAKF(a)
where a = VOUT
VPEAK
and
F(a)≈-0.411a4+0.296a3-0.312a2+0.638a-0.0000846,
{a|0~0.7}
RT8417
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
DS8417-00 August 2017 www.richtek.com 9
The inductance range is showed as below :
L = VOUTTOFF
IPEAK =
(VPEAK-VOUT)TON
IPEAK
Where 1s TON 35s and 2s TOFF 40s
The frequency at the top of the sine wave can be
calculated :
fSW = 1
TON+TOFF+TDELAY
(TDELAY is set up about 1s)
Forward Diode Selection
When the power switch turns off, the path for the
current is through the diode connected between the
switch output and ground. This forward biased diode
must have minimum voltage drop and recovery time.
The reverse voltage rating of the diode should be
greater than the maximum input voltage and the
current rating should be greater than the maximum
load current.
The peak voltage stress of diode is :
VD = 1.2 2 VAC MAX = 1.2 2 264 = 448V
The input source is universal (VIN = 85V to 264V), VD
will reach 448V.
MOSFET Selection
The peak current through this MOSFET will be over the
maximum output current. This component current
rating should be greater than 1.2 times the maximum
load current and the reverse voltage rating of the
MOSFET should be greater than 1.2 times the
maximum input voltage, assuming a ±20% output
current ripple.
The peak voltage rating of the MOSFET is :
VQ1 = 1.2 2 VAC MAX = 1.2 2 264 = 448V
The largest peak current will occur at the highest VIN.
The current rating of MOSFET is determined by the
OCP threshold which is about seven times of the sense
voltage threshold.
Thermal Protection (OTP)
A thermal protection feature is included to protect the
RT8417 from excessive heat damage. When the
junction temperature exceeds a threshold of 150°C
(typ.), the thermal protection OTP will be triggered and
the GATE will be turned off.
Thermal Considerations
The junction temperature should never exceed the
absolute maximum junction temperature TJ(MAX), listed
under Absolute Maximum Ratings, to avoid permanent
damage to the device. The maximum allowable power
dissipation depends on the thermal resistance of the IC
package, the PCB layout, the rate of surrounding
airflow, and the difference between the junction and
ambient temperatures. The maximum power
dissipation can be calculated using the following
formula :
PD(MAX) = (TJ(MAX) TA) / JA
where TJ(MAX) is the maximum junction temperature,
TA is the ambient temperature, and JA is the
junction-to-ambient thermal resistance.
For continuous operation, the maximum operating
junction temperature indicated under Recommended
Operating Conditions is 125C. The junction-to-
ambient thermal resistance, JA, is highly package
dependent. For a SOP-8 package, the thermal
resistance, JA, is 188C/W on a standard JEDEC 51-7
high effective-thermal-conductivity four-layer test board.
The maximum power dissipation at TA = 25C can be
calculated as below :
PD(MAX) = (125C 25C) / (188C/W) = 0.53W for a
SOP-8 package.
The maximum power dissipation depends on the
operating ambient temperature for the fixed TJ(MAX)
and the thermal resistance, JA. The derating curves in
Figure 1 allows the designer to see the effect of rising
ambient temperature on the maximum power
dissipation.
RT8417
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
www.richtek.com DS8417-00 August 2017 10
Figure 1. Derating Curve of Maximum Power
Dissipation
Layout Considerations
For best performance of the RT8417, the following
layout guidelines should be strictly followed.
The capacitor, CVCC and CVC, must be placed as
close as possible to the VCC and VC pin.
The IC GATE and GND pin are high frequency
switching nodes. Both traces must be as wide and
short as possible.
Keep the main traces with switching current as short
and wide as possible.
Place L, Q1, RSENSE, COUT, and D1 as close to each
other as possible.
DMG
VC
GND
VCC
HV
NC
GATE
SENSE
RT8417
1 8
7
6
54
3
2
CVCC
CVC
Bridge Rectifier
RHV
10k
RSENSE
RDMG1
RDMG2
CDMG
CIN
L
Q1
COUT
RG
Line
Neutral
DMG
Place the Components CVC and CVCC as
close as possible to the IC
Analog GND
Narrow trace from main circuit
to the IC to avoid the switching
noise
Applying the Kelvin sense trace to
increase the current accuracy
Place the MOSFET Q1, the Diode D1 and the
resistor RSENSE as close as possible to the
each other
D1
GND
Figure 2. PCB Layout Guide
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0 25 50 75 100 125
Ambient Temperature (°C)
Ma
xim
um
Po
we
r D
issip
atio
n (
W) 1 Four-Layer PCB
RT8417
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DS8417-00 August 2017 www.richtek.com 11
Outline Dimension
Symbol Dimensions In Millimeters Dimensions In Inches
Min Max Min Max
A 4.801 5.004 0.189 0.197
B 3.810 3.988 0.150 0.157
C 1.346 1.753 0.053 0.069
D 0.330 0.508 0.013 0.020
F 1.194 1.346 0.047 0.053
H 0.170 0.254 0.007 0.010
I 0.050 0.254 0.002 0.010
J 5.791 6.200 0.228 0.244
M 0.400 1.270 0.016 0.050
8-Lead SOP Plastic Package
RT8417
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
www.richtek.com DS8417-00 August 2017 12
Footprint Information
Package Number of Pin Footprint Dimension (mm)
Tolerance P A B C D M
SOP-8 8 1.27 6.80 4.20 1.30 0.70 4.51 ±0.10
Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st 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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