RT8487
High Efficiency BCM LED Driver Controller for High Power
Factor Offline Applications
General Description
Features
The RT8487 is a Boundary mode high PF floating buck
constant LED current output controller with an internal
gate driver.
The RT8487 features a ZCS detector which keeps
and
Programmable Constant LED Current with Highly
Extremely Low Quiescent Current Consumption
True Low System BOM Cost and Economical
Unique Programmable AND Pin for ZVS Setting
to Achieve Best Power Efficiency
Especially, the RT8487 can use a cheap simple drum
Universal Input Voltage Range with Off-Line
Topology
core inductor in the system instead of an EE core to
Built-in Over Thermal Protection
obtain high efficiency.
Built-in Over Voltage Protection
The RT8487 is housed in a TSOT-23-6 package. Thus,
Output LED String Open Protection
the components in the whole LED driver system can be
Output LED String Short Protection
made very compact.
Output LED String Over Current Protection
Ordering Information
Applications
RT8487
Package Type
J6 : TSOT-23-6
Lead Plating System
G : Green (Halogen Free and Pb Free)
THDi
Floating Buck Converter Solution
circuit which has minimized system component counts;
saved both PCB size and total system cost.
Factor
and 1µA Shutdown Current
(PFC) and low total harmonic distortion of current
(THDi) by a smart internal line voltage compensation
Power
Precision Current Regulation
power efficiency, better EMI performance.
The RT8487 achieves high power factor correction
High
Consideration Applications
system operating in BCM and obtaining excellent
Support
E27, PAR, Light Bar, Offline LED Lights
Pin Configurations
(TOP VIEW)
SENSE VC AND
6
5
4
2
3
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.
VCC GND GATE
TSOT-23-6
Marking Information
00=DNN
00= : Product Code
DNN : Date Code
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS8487-00
March 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT8487
Simplified Application Circuit
Buck type:
Bridge Rectifier
+
R1
R2
CIN
AND
VCC
RT8487
VC
GATE
R3B
C1
GND
Q1
SENSE
D2
Bootstrap Diode
C2
RS
L1
D1
COUT
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RT8487
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
VCC
Supply Voltage Input. For good bypass, a ceramic capacitor near the VCC
pin is required.
2
GND
Ground.
3
GATE
Gate Driver Output for External MOSFET Switch.
4
AND
AND Function Pin.
5
VC
Close Loop Compensation Node.
6
SENSE
LED Current Sense Input. The typical sensing threshold is 250mV between
the SENSE and GND pin.
Function Block Diagram
VCC
Regulator
+
EA
-
SENSE
V
State Machine
250mV
A
GATE
GND
VC
AND
Operation
The RT8487 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 / THDi,
proper selection of a compensation network is needed.
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March 2015
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RT8487
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage (VCC) -----------------------------------------------------------------------------------------40V
Power Dissipation, PD @ TA = 25C
TSOT-23-6 ---------------------------------------------------------------------------------------------------------------0.5W
Package Thermal Resistance
(Note 2)
TSOT-23-6, JA ---------------------------------------------------------------------------------------------------------197.4C/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
MM (Machine Model) --------------------------------------------------------------------------------------------------200V
Recommended Operating Conditions
(Note 4)
Supply Input Voltage, VCC ------------------------------------------------------------------------------------------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 Shutdown Current
ISD
VCC = VUVLO_ON 3V
--
--
1
A
VCC Quiescent Current
IQC
Gate stands still
--
0.5
5
mA
VCC Operating Current
ICC
By CGATE = 1nF, Freq.= 20kHz
--
1
5
mA
VCC OVP Level
VOVP
--
34
--
V
Sense Pin Leakage Current
ISENSE
--
1
5
A
Current Sense Threshold
VSENSE
242.5
250
257.5
mV
AND Pin Leakage Current
IAND
--
1
2
A
GATE Voltage High
VGATE_H
IGATE = 0mA
10.5
12
--
IGATE = 10mA
9
10
--
GATE Driver
VSENSE = 3V
VAND = 5V
Rising Time
tr
--
50
--
Falling Time
tf
--
25
--
V
ns
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 at TA = 25C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.
Note 3. Devices are ESD sensitive. Handling precaution recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
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is a registered trademark of Richtek Technology Corporation.
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March 2015
RT8487
Typical Application Circuit
Buck :
Bridge Rectifier
+
-
R1
511K
R2
511K
CIN
0.1μF/500V
4
5
R3B
100k
C1
4.7μF/50V
1
AND
VC
2
GND
C2
1μF
VCC
RT8487
3
GATE
SENSE
6
Q1
MTN4N60
RS
0.8
D1
ES2J
RB
10
L1
470μH
D2
RS1M
COUT
270μF/63V
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RT8487
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
-25
0
50
75
100
125
100
125
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
-25
0
25
50
75
100
-50
125
-25
0
Sense Threshold vs. Supply Voltage
450
450
400
400
Sense Threshold (mV)
500
350
300
250
200
150
100
300
250
200
150
100
50
0
0
20
30
Supply Voltage (V)
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75
350
50
10
50
Sense Threshold vs. Temperature
500
0
25
Temperature (°C)
Temperature (°C)
Sense Threshold (mV)
25
Temperature (°C)
Supply Voltage (V)
40
VCC = 24V
-50
0
50
100
150
Temperature (°C)
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RT8487
Efficiency vs. Input Voltage
Output Current vs. Input Voltage
100
350
340
Output Current (mA)
Efficiency (%)
95
90
85
VIN_AC = 90V to 264V
80
330
320
310
300
290
280
VIN_AC = 90V to 264V
270
IOUT = 300mA, LED 14pcs,
L = 470μH
IOUT = 300mA, LED 14pcs,
L = 470μH
260
75
250
85
105
125
145
165
185
205
225
245
265
85
105
125
145
165
185
225
Input Voltage (V)
Power Factor vs. Input Voltage
Input and Output Current
1.00
245
265
VIN_AC = 264V
0.95
Power Factor
205
Input Voltage (V)
VIN
(500V/Div)
0.90
IIN
(200mA/Div)
0.85
0.80
VOUT
(50V/Div)
VIN_AC = 90V to 264V
0.75
IOUT = 300mA, LED 14pcs,
L = 470μH
IOUT
(500mA/Div)
0.70
85
105
125
145
165
185
205
225
245
265
IOUT = 300mA, LED 14pcs, L = 470μH
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)
IOUT = 300mA,
LED 14pcs, L = 470μH
VOUT
(20V/Div)
IOUT = 300mA,
LED 14pcs, L = 470μH
IOUT
(200mA/Div)
Time (100ms/Div)
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March 2015
IOUT
(200mA/Div)
Time (100ms/Div)
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RT8487
Total Harmonic Distortion
Total Harmonic Distortion
50%
50%
45%
Class C
Measured
40%
VIN_AC = 115V/60Hz
45%
IOUT = 300mA, LED 14pcs,
L = 470μH
40%
35%
35%
30%
30%
25%
25%
20%
20%
15%
15%
10%
10%
5%
5%
Class C
Measured
VIN_AC = 230V/50Hz
IOUT = 300mA, LED 14pcs,
L = 470μH
0%
0%
3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
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3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
is a registered trademark of Richtek Technology Corporation.
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RT8487
Application Information
RT8487 is a boundary mode, high efficiency constant
up current exceeds certain minimum value. Otherwise,
current controller with internal high side driver, which
the RT8487 may latch off and the system will never
can be used in buck and buck-boost configuration, to
start. The start-up current equals
provide a constant output current to the (LED) load. It
contains special circuitry for achieving high power
(for 110VAC regions), and equals
factor and low input current THD, while minimizing
external
component
2 90V / R1 +R2
2 180V / R1 +R2
count. The small SOT23-6
(for 220VAC regions). The typical required minimum
package keeps application footprint small, and makes
start-up current is 100A. The typical total start up
RT8487 a cost effective solution for off-line LED
resistance (R1 + R2) is around 1M Ohm for universal
drivers.
inputs.
The RT8487 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)
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
2 VAC(MAX)
The RT8487 includes a UVLO function with 10.8V
where VAC(MAX) is the maximum input voltage (RMS)
hysteresis.
and the parameter 1.2 is used for safety margin.
For system start up, the VIN must rise over 18V (typ.)
For this example :
to turn on the GATE terminal.
VBR = 1.2
The GATE terminal will turn off if VIN falls below 7.2V
(typ.)
2 VAC(MAX) = 1.2 2 264 = 448V
If the input source is universal, VBR will reach 448V. In
Setting Average Output Current
this case, a 600V, 0.5A bridge rectifier can be chosen.
The output current that flows through the LED string is
Input Capacitor Selection
set by an external resistor, RS, which is connected
For High Power Factor application, the input Capacitor
between
CIN should use a small value capacitance to achieve
the GND and SENSE pins. The relationship between
line voltage sine-wave.
output current, IOUT, and RS is shown below :
The voltage rating of the input filter capacitor, VCIN,
IOUT =
250
mA
RS
should be large enough to handle the input voltage.
VIN 1.2
2 VAC(MAX) = 1.2 2 264 = 448V
Start-Up Resistor
The start-up resistor should be chosen to set the start
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RT8487
Thus, a 0.1F / 500V film capacitor can be chosen in
Tresonance = L1 CSW
this case.
where CSW is the capacitance at the switch node,
mostly determined by the MOSFET drain-source
Inductor Selection
For high power factor application, the RT8487 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 :
IPEAK
2Pin
=
VPEAKF a
where a =
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
TDELAY (μs)=(-0.4 x R3B +3500 x R3B+407500) x 10
-6
R3B resister value in k.
Forward Diode Selection
When the power switch turns off, the path for the
VOUT
VPEAK
current is through the diode connected between the
and
switch output and ground. This forward biased diode
F a -0.411a +0.296a -0.312a +0.638a-0.0000846,
must have minimum voltage drop and recovery time.
a|0~0.7
The reverse voltage rating of the diode should be
The inductance range is showed as below :
greater than the maximum input voltage and the
VOUT TON
V
VOUT TOFF
= PEAK
IPEAK
IPEAK
current rating should be greater than the maximum
4
L=
3
2
load current.
Where 0.5s TON 35s and 2s TOFF 30s
The peak voltage stress of diode is :
The frequency at the top of the sine wave can be
VD 1.2
calculated :
fSW =
1
TON + TOFF + TDELAY
(TDELAY is determined by the resistor connected to
AND pin , see Turn on delay time)
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
Turn On Delay Time
maximum output current. This component current
After the inductor current has reached zero, a
rating
resonance will occur between the inductor and the
should be greater than 1.2 times the maximum load
MOSFET drain-source capacitance.
current and the reverse voltage rating of the MOSFET
In order to minimize the MOSFET switching losses,
should be greater than 1.2 times the maximum input
RT8487 provides the flexibility to adjust the delay time
voltage, assuming a ±20% output current ripple.
of next switch-on cycle in order to switch-on at the
The peak voltage rating of the MOSFET is :
maximum point of the resonance, which corresponds to
VQ1 = 1.2
the minimum drain-source voltage value.
2 VAC(MAX) = 1.2
2 264 = 448V
The delay time from zero current point to the maximum
The largest peak current will occur at the highest VIN.
of the switch resonance which can be calculated from :
The current rating of MOSFET is determined by the
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RT8487
OCP threshold which is about seven times of the sense
voltage threshold.
Maximum Power Dissipation (W)1
0.6
Thermal Protection (OTP)
A thermal protection feature is included to protect the
RT8487 from excessive heat damage. When the
junction
temperature exceeds a threshold of 150C, the thermal
protection OTP will be triggered and the GATE will be
turned off.
Four-Layer PCB
0.5
0.4
0.3
0.2
0.1
0.0
0
Thermal Considerations
25
50
75
100
125
Ambient Temperature (°C)
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
Figure 1. Derating Curve of Maximum Power
dissipation depends on the thermal resistance of the IC
Dissipation
package, PCB layout, rate of surrounding airflow, and
Layout Considerations
difference between junction and ambient temperature.
For best performance of the RT8487, the following
The maximum power dissipation can be calculated by
layout guidelines should be strictly followed.
the following formula :
PD(MAX) = (TJ(MAX) TA) / JA
where TJ(MAX) is the maximum junction temperature,
The hold up capacitor, C1, must be placed as close
as possible to the VCC pin.
The compensation capacitor, C2, and delay resistor,
TA is the ambient temperature, and JA is the junction to
R3B, must be placed as close as possible to the VC
ambient thermal resistance.
and the AND pin.
For recommended operating condition specifications,
The IC GATE and GND pin are high frequency
the maximum junction temperature is 125C. The
switching nodes.
junction to ambient thermal resistance, JA, is layout
short as possible.
dependent. For TSOT-23-6 package, the thermal
resistance, JA, is 197.4C/W on a standard JEDEC
51-7 four-layer thermal test board. The maximum
power dissipation at TA = 25C can be calculated by
Both traces must be as wide and
Keep the main traces with switching current as short
and wide as possible.
Place CIN, L1, Q1, RS, COUT, and D1 as close to
each other as possible.
the following formula :
PD(MAX) = (125C 25C) / (197.4C/W) = 0.5W for
TSOT-23-6 package
The maximum power dissipation depends on the
operating ambient temperature for fixed TJ(MAX) and
thermal resistance, JA. The derating curve in Figure 1
allows the designer to see the effect of rising ambient
temperature on the maximum power dissipation.
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RT8487
Place the compensation
Components C2 and R3B as
close as possible to the IC
VMAIN
R1
C2
Place the MOSFET Q1, the
Diode D1 and the resistor RS
as close as possible to the
each other
R3B
R2
SENSE
6
VC
5
AND
4
RT8487
CIN
2
GND
1
VCC
3
GATE
VCC RB ZD(Option)
Q1
RG
RS
C1
SENSE
Analog GND
L1
D2
LED+
Analog GND
COUT
D1
LED-
Power GND
Place the capacitor
C1 as close as possible
to the VCC pin
Kelvin sense from the sense resistor
directly from the sense resistor is
necessary to avoid the sense threshold
setting error by the parasitic PCB trace
resistance.
Narrow trace from
main circuit to the IC
to avoid the
switching noise
Figure 2. PCB Layout Guide
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RT8487
Outline Dimension
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.700
1.000
0.028
0.039
A1
0.000
0.100
0.000
0.004
B
1.397
1.803
0.055
0.071
b
0.300
0.559
0.012
0.022
C
2.591
3.000
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
TSOT-23-6 Surface Mount 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.
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