RT8417 - Richtek Technology Corporation · RT8417 Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation

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


www.richtek.com DS8417-00 August 2017 2

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



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



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



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



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



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



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



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



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



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



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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RT8417 - Richtek Technology Corporation · RT8417 Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation