RT8497
Power MOSFET Integrated High Efficiency BCM LED Driver
Controller for High Power Factor Applications
General Description
Features
The RT8497 integrates a power MOSFET and a
Boundary mode controller. It is used for step down
converters by well controlling the internal MOSFET and
regulating a constant output current.
The RT8497 features a ZCS detector which keeps
system operating in BCM and obtaining excellent
power efficiency, better EMI performance.
The RT8497 achieves high Power Factor Correction
(PFC) and low Total Harmonic Distortion of Current
(THDi) by a smart internal line voltage compensation
circuit which has minimized system component counts;
saved both PCB size and total system cost.
Especially, the RT8497 can use a cheap simple drum
core inductor in the system instead of an EE core to
obtain high efficiency.
The RT8497 is housed in a SOP-8 package. Thus, the
components in the whole LED driver system can be
made very compact.
Ordering Information
Built-In Power MOSFET
Support High Power Factor and Low THDi
Applications
Programmable Constant LED Current with
High-Precision Current Regulation
Extremely Low Quiescent Current Consumption
and 1A Shutdown Current
Compact Floating Buck Topology with Low
Component Counts, Small PCB Size, and Low
System BOM Cost
Unique Programmable AND Pin for ZVS Setting
to Achieve Best Power Efficiency
Support Off-Line Universal Input Voltage Range
Built-in Over Thermal Protection
Built-in Over Voltage Protection
Output LED String Open Protection
Output LED String Short Protection
Output LED String Over Current Protection
Applications
E27, PAR, Light Bar, Offline LED Lights
RT8497
Package Type
S : SOP-8
Lead Plating System
G : Green (Halogen Free and Pb Free)
MOSFET Built-In
Default : 500V/5.2
A : 500V/2
B : 600V/4.2
C : 600V/7
D : 600/3.2
Pin Configuration
(TOP VIEW)
8
SGND
VCC
VC
2
7
NC
AND
3
6
DRAIN
SOURCE
4
5
DRAIN
SOP-8
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
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
DS8497-03
July 2017
is a registered trademark of Richtek Technology Corporation.
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1
RT8497
Marking Information
RT8497GS
RT8497
GSYMDNN
RT8497AGS
RT8497GS : Product Number
YMDNN : Date Code
RT8497BGS
RT8497B
GSYMDNN
RT8497A
GSYMDNN
RT8497AGS : Product Number
YMDNN : Date Code
RT8497CGS
RT8497BGS : Product Number
YMDNN : Date Code
RT8497C
GSYMDNN
RT8497CGS : Product Number
YMDNN : Date Code
RT8497DGS
RT8497D
GSYMDNN
RT8497DGS : Product Number
YMDNN : Date Code
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
SGND
Ground of the chip.
2
VC
Close Loop compensation node.
3
AND
Next delay timing function control.
4
SOURCE
Internal power MOSFET source connection.
DRAIN
Internal power MOSFET drain connection.
7
NC
No internal connection.
8
VCC
Supply voltage input of the chip. For good bypass, a ceramic capacitor near the
VCC pin is required.
5, 6
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is a registered trademark of Richtek Technology Corporation.
DS8497-03
July 2017
RT8497
Functional Block Diagram
VCC
Regulator
SOURCE
DRAIN
+
EA
-
+
-
State
Machine
A
SOURCE
250mV
SGND
VC
AND
Operation
The RT8497 senses true average output current and
system and dominates the frequency response. To
keeps the system driving constant output current. The
stabilize the system and achieve better PFC / THDi,
VC pin is the compensation node in this close loop
proper selection of a compensation network is needed.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
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July 2017
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RT8497
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage ------------------------------------------------------------------------------------------------ 0.3V to 40V
DRAIN to SOURCE Voltage, VDS, (RT8497B, RT8497C, RT8497D) ---------------------------------- 0.3V to 600V
DRAIN to SOURCE Voltage, VDS, (RT8497, RT8497A) -------------------------------------------------- 0.3V to 500V
DRAIN Current, ID @ TC = 25C -------------------------------------------------------------------------------- 1.4A
DRAIN Current, ID @ TC = 100C ------------------------------------------------------------------------------ 0.9A
Power Dissipation, PD @ TA = 25C
SOP-8 ------------------------------------------------------------------------------------------------------------------- 0.53W
Package Thermal Resistance
(Note 2)
SOP-8, JA ------------------------------------------------------------------------------------------------------------- 188C/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
VCC UVLO ON
VUVLO_ON
17
18
19
V
VCC UVLO OFF
VUVLO_OFF
6.4
7.2
8
V
VCC Shut Down Current
ISHDN
VCC = 15V
--
--
1
A
VCC Quiescent Current
IQ
Drain stands still
--
0.5
5
mA
VCC Operating Current
ICC
By CGATE = 1nF, Freq. = 20kHz
--
1
5
mA
VCC OVP Level
VOVP
31.5
34
38.5
V
Current Sense Threshold
VSENSE
242.5
250
257.5
mV
AND Pin Leakage Current
IAND
--
1
2
A
RT8497
--
5.2
--
RT8497A
--
2
--
RT8497B
--
4.2
--
RT8497C
--
7
--
RT8497D
--
3.2
--
Static Drain-Source
On-Resistance
RDS(ON)
VAND = 5V
VGS = 12V, ID
= 100mA
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is a registered trademark of Richtek Technology Corporation.
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July 2017
RT8497
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
--
10
A
RT8497, VDS = 500V
RT8497A, VDS = 500V
Drain-Source Leakage Current IDSS
RT8497B, VDS = 600V
RT8497C, VDS = 600V
RT8497D, VDS = 600V
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.
Note 3. Devices are ESD sensitive. Handling precaution recommended.
Note 4. The device is not guaranteed to function outside its operating conditions
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
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July 2017
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RT8497
Typical Application Circuit
Bridge Rectifier
+
-
CIN
R1
5, 6
3
R3
(Optional)
C1
C2
2
DRAIN
VCC 8
AND
RT8497
Optional
VC
1 SGND
SOURCE
4
D2
Bootstrap diode
R2
L1
+
D1
EC1
Figure 1. Typical Application of Buck Type
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RT8497
Typical Operating Characteristics
Operating Current vs. Temperature
2.0
1.8
1.8
Operating Current (mA)
Operating Current (mA)
Operating Current vs. Supply Voltage
2.0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
GATE with 1nF
VCC = 24V, GATE with 1nF
0.0
0.0
0
10
20
30
-50
40
0
100
150
UVLO vs. Temperature
40
20
39
18
38
16
37
14
UVLO (V)
OVP (V)
OVP vs. Temperature
36
35
34
UVLO_ON
12
10
8
33
6
32
4
31
2
UVLO_OFF
0
30
-50
-30
-10
10
30
50
70
90
-50
110 130 150
0
Sense Threshold vs. Supply Voltage
450
450
Sense Threshold (mV)
500
400
350
300
250
200
150
100
350
300
250
200
150
100
50
0
0
20
30
40
Supply Voltage (V)
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July 2017
150
400
50
10
100
Sense Threshold vs. Temperature
500
0
50
Temperature (°C)
Temperature (°C)
Sense Threshold (mV)
50
Temperature (°C)
Supply Voltage (V)
VCC = 24V
-50
0
50
100
150
Temperature (°C)
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RT8497
Efficiency vs. Input Voltage
Output Current vs. Input Voltage
100
370
RT8497A
RT8497A
Output Current (mA)
Efficiency (%)
95
90
85
VIN_AC = 90V to 264V
80
360
350
340
330
320
310
300
VIN_AC = 90V to 264V
290
IOUT = 320mA, LED 16pcs,
L = 470μH
IOUT = 320mA, LED 16pcs,
L = 470μH
280
270
75
85
105
125
145
165
185
205
225
245
85
265
105
125
145
165
185
205
225
245
265
Input Voltage (V)
Input Voltage (V)
Input and Output Current
Power Factor vs. Input Voltage
1.00
RT8497A
Power Factor
0.95
VIN_AC = 264V
VIN
(500V/Div)
0.90
IIN
(200mA/Div)
0.85
0.80
VOUT
(50V/Div)
VIN_AC = 90V to 264V
0.75
IOUT = 320mA, LED 16pcs,
L = 470μH
IOUT
(500mA/Div)
0.70
85
105
125
145
165
185
205
225
245
IOUT = 320mA, LED 16pcs, L = 470μH
265
Time (5ms/Div)
Input Voltage (V)
Power Off
Power On
VIN_AC = 264V
VIN_AC = 264V
VIN
(500V/Div
VIN
(500V/Div)
VOUT
(20V/Div)
VOUT
(20V/Div)
IOUT
(200mA/Div)
IOUT = 320mA,
LED 16pcs, L = 470μH
Time (100ms/Div)
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IOUT
(200mA/Div)
IOUT = 320mA,
LED 16pcs, L = 470μH
Time (100ms/Div)
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July 2017
RT8497
Total Harmonic Distortion
50%
45%
Class C
Measured
VIN_AC = 115V
IOUT = 320mA, LED 16pcs,
L = 470μH
40%
Total Harmonic Distortion
50%
45%
40%
35%
35%
30%
30%
25%
25%
20%
20%
15%
15%
10%
10%
5%
5%
0%
Class C
Measured
VIN_AC = 230V
IOUT = 320mA, LED 16pcs,
L = 470μH
0%
3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
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July 2017
3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
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RT8497
Application Information
The RT8497 is a Boundary mode converter, which can
be used in buck configuration, to provide a constant
output current to the (LED) load. It contains special
circuitry for achieving high power factor and low input
current THD, while minimizing external component
count. The RT8497 integrates a power MOSFET and
housed in a SOP-8 package. Thus, the components in
the whole LED driver system can be made very
compact.
The RT8497 can achieve high accuracy LED output
current via the average current feedback loop control.
The internal sense voltage (250mV typ.) is used to set
the average output current. The average current is set
by the external resistor, RS. 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 RT8497 includes a UVLO function with 10.8V
hysteresis. For system start up, the VIN must rise over
18V (typ.) to turn on the internal MOSFET. The internal
MOSFET will turn off if VIN falls below 7.2V (typ.)
Setting Average Output Current
The output current that flows through the LED string is
set by an external resistor, RS, which is connected
between the GND and SOURCE pins. The relationship
between output current, IOUT, and RS is shown below :
IOUT =
250
mA
RS
Start-up Resistor
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, on the other hand, is only dependent on
the input voltage. Thus, the VBR rating is calculated as
below :
VBR = 1.2
start.
2 90V / R1 +R2 (for
The start-up current equals
2 180V / R1 +R2
110VAC regions), and equals
(for 220VAC regions). The typical required minimum
start-up current is 100A. The typical total start up
resistance (R1+ R2) is around 1M Ohm for universal
inputs.
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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. In
this case, a 600V, 0.5A bridge rectifier can be chosen.
Input Capacitor Selection
For High Power Factor application, the input Capacitor
CIN should use a small value capacitance to achieve
line voltage sine-wave.
The voltage rating of the input filter capacitor, VCIN,
should be large enough to handle the input voltage.
VCIN ≥ (1.2× 2 × VAC(MAX) ) = (1.2× 2 × 264) = 448V
Thus, a 0.1F / 500V film capacitor can be chosen in
this case.
Inductor Selection
For high power factor application, the RT8497 operates
the converter in BCM (Boundary-Condition Mode). 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 below :
The start-up resistor should be chosen to set the start
up current exceeds certain minimum value. Otherwise,
the RT8497 may latch off and the system will never
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
The inductance range is showed as below :
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DS8497-03
July 2017
RT8497
L=
VOUT TON
V
VOUT TOFF
= PEAK
IPEAK
IPEAK
VD 1.2
2 VAC(MAX) = 1.2
2 264 = 448V
The input source is universal (VIN = 85V to 264V), VD
will reach 448V.
Where 0.5s TON 35s and 2s TOFF 30s
The frequency at the top of the sine wave can be
calculated :
fSW =
1
TON + TOFF + TDELAY
(Tdelay is determined by the resistor connected to AND
pin , see Turn on delay time)
Thermal Protection (OTP)
A thermal protection feature is included to protect the
RT8497 from excessive heat damage. When the
junction temperature exceeds a threshold of 150°C, the
thermal protection OTP will be triggered and the
internal MOSFET will be turned off.
Thermal Considerations
Turn On Delay Time
After the inductor current has reached zero, a
resonance will occur between the inductor and the
MOSFET drain-source capacitance.
In order to minimize the MOSFET switching losses, the
RT8497 provides the flexibility to adjust the delay time
of next switch-on cycle in order to switch-on at the
maximum point of the resonance, which corresponds to
the minimum drain-source voltage value.
The delay time from zero current point to the maximum
of the switch resonance which can be calculated from :
Tresonance = L1 CSW
where CSW is the capacitance at the switch node,
mostly determined by the MOSFET drain-source
capacitance.
The delay time TDELAY from zero current detection
point to next MOSFET switch-on cycle can be adjusted
by the resistor value R3B connected between AND pin
and IC GND
2
-6
TDELAY (μs)=(-0.4 x R3B +3500 x R3B+407500) x 10
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-toambient 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
R3B resister value in k.
high effective-thermal-conductivity four-layer test board.
The maximum power dissipation at TA = 25C can be
Forward Diode Selection
calculated as below :
When the power switch turns off, the path for the
PD(MAX) = (125C 25C) / (188C/W) = 0.53W for a
SOP-8 package.
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 maximum power dissipation depends on the
operating ambient temperature for the fixed TJ(MAX)
and the thermal resistance, JA. The derating curves in
Figure 2 allows the designer to see the effect of rising
ambient temperature on the maximum power
dissipation.
The peak voltage stress of diode is :
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July 2017
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RT8497
Layout Considerations
For best performance of the RT8497, the following
Maximum Power Dissipation (W)1
1.0
Four-Layer PCB
0.9
layout guidelines should be strictly followed.
The hold up capacitor, C1, must be placed as close as
possible to the VCC pin.
0.8
0.7
0.6
The compensation capacitor, C2, and delay resistor,
0.5
R3B, must be placed as close as possible to the VC
and the AND pin.
0.4
0.3
The IC SOURCE pin are high frequency switching
nodes. The traces must be as wide and short as
possible.
0.2
0.1
0.0
0
25
50
75
100
Keep the main traces with switching current as short
125
Ambient Temperature (°C)
and wide as possible.
Place CIN, L1, RS, COUT, and D1 as close to each
other as possible.
Figure 2. Derating Curve of Maximum Power
Dissipation
Kelvin sense from the sense resistor
directly from the bottom end of the
sense resistor is necessary to avoid
the sense threshold setting error by the
parasitic PCB trace resistance.
Place the capacitor
C1 as close as possible
to the VCC pin
VMAIN
R1
7
6
5
DRAIN
DRAIN
VCC
8
NC
R2
RT8497
GND
VC
AND
SOURCE
C1
CIN
1
2
3
4
VCC RB ZD(Option)
RS
L1
D2
LED+
C2
Analog GND
Analog GND
R3B
COUT
D1
LED-
Power GND
Place the compensation
Place the Diode D1 and the
Components C2 and R3B as resistor RS as close as
close as possible to the IC
possible to the SOURCE pin
Narrow trace from
main circuit to the IC
to avoid the
switching noise
Figure 3. PCB Layout Guide
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RT8497
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
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.
Copyright © 2017 Richtek Technology Corporation. All rights reserved.
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July 2017
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