RT8560A

RT8560A
High Voltage 4 Channel LED Driver
General Description
Features
The RT8560A is a 60V 4-channel LED driver capable of
delivering 30mA to each channel with 15 LEDs (3.6V per
diode) total 60 LEDs with one driver. The RT8560A is a
current mode boost converter opearated at 1MHz switching
frequency, wide VIN range covers from 6V to 40V and the
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High Voltage : VIN up to 40V, VOUT up to 60V, Driving
up to 60 x 3.6V LEDs (15 each channel)
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on-chip current switch is rated at 1.5A.
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Channel Current Programmabe 4mA to 30mA and
Matched to 3% Accuracy
Current Mode PWM 1MHz Boost Converter
Easy Analog and Digital Dimming Control
Programmable Soft Start
Automatic Detecting Unconnected and/or Broken
Channel
Programmable Over Voltage Protection
Disconnects LED in Digital Dimming : Providing
High Accuracy Digital Dimming by PWM at ACTL
Pin or EN Pin
VIN Under Voltage Lockout
Over Temperature Protection
Current Limiting Protection
Small 20-Lead WQFN Package
RoHS Compliant and Halogen Free
The PWM output voltage loop selects and regulates the
LED pin with the highest voltage string to 0.9V allowing
voltage mismatches between LED strings. The RT8560A
automatically detects and disconnects any unconnected
and/or broken strings during operation from PWM loop to
prevent VOUT from over voltage.
The 3% matched LED currents on all channels are simply
programmed with a resistor or a current sink. Both analog
dimming and digitally controlled PWM dimming are
supported by RT8560A. Analog dimming is linearly
controlled by an external voltage. With an on-chip output
clampping amplifier and a 200kΩ resistor, PWM dimming
signal is easily low-pass filtered to an analog dimming
signal with one external capacitor for noise-free PWM
dimming. A very high contrast ratio true digital PWM
dimming can be achieved by driving EN pin to PWM
shutdown the chip or by driving ACTL pin.
Other protecting features include programmable PWM
output over voltage protection, LED curren limit, PWM
switch current limit and thermal shutdown. The RT8560A
is packaged with a tiny footprint package of WQFN-20L
4x4 packages.
LED1
LED2
LED3
17
16
2
GND
20 19 18
GND
GND
GND
SW
SW
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Applications
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UMPC and Notebook Computer Backlight
GPS, Portable DVD Backlight
Desk Lights and Room Lighting
Ordering Information
RT8560A
Package Type
QW : WQFN-20L 4x4 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
`
13
12
21
11
6
7
8
9
VCC2
VCC1
RISET
ACTL
DCTL
5
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
14
GND
4
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`
15
3
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Richtek products are :
(TOP VIEW)
1
z
Note :
Pin Configurations
GND
z
10
LED4
VC
SS
OVP
EN
Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
WQFN-20L 4x4
DS8560A-01 April 2011
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1
RT8560A
Typical Application Circuit
VIN
6V to 40V
COUT3
1µF
L
10µH
VOUT
60V MAX
D
CVIN
10µF
RVCC1
10
C2
15 LED String
RT8560A
R4
4, 5 SW
LED1
7 VCC1
CVCC1
1µF
R3
1k
5V
R1
VOUT
VIN
:
:
:
:
COUT1 COUT2
18
LED4 15
RISET
5.36k
OVP
R2
RISET
RVCC2
10
:
:
:
:
:
:
:
:
LED2 17
LED3 16
11 EN
12
:
:
:
:
6 VCC2
8
5.36k
RISET
R5
1k
ACTL 9
CVCC2
1µF
ILED = 20mA ×
PWM Signal
DCTL 10
14
VC
13 SS
RVC
1.8k
CVC
3.9nF
GND
1, 2, 3, 19, 20, Exposed Pad (21)
C1
0.1µF
Figure 1. 1MHz, 20mA Full Scale Current Digital PWM Dimming Control
VIN
6V to 40V
COUT3
1µF
L
10µH
VOUT
60V MAX
D
CVIN
10µF
RVCC1
10
C2
15 LED String
RT8560A
R4
4, 5 SW
7 VCC1
CVCC1
1µF
5V
R3
1k
R1
VOUT
LED2 17
LED3 16
12
LED4 15
OVP
RISET
RVCC2
10
8
6 VCC2
ACTL 9
DCTL 10
CVCC2
1µF
:
:
:
:
:
:
:
:
:
:
:
:
COUT1 COUT2
18
11 EN
R2
VIN
LED1
:
:
:
:
RISET
5.36k
R5
1k
ILED = 20mA ×
5.36k
RISET
Analog
Dimming
14
RVC
1.8k
CVC
3.9nF
VC
13 SS
GND
1, 2, 3, 19, 20, Exposed Pad (21)
C1
0.1µF
Figure 2. 1MHz, 20mA Full Scale Current Analog Dimming Control
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DS8560A-01 April 2011
RT8560A
VIN
6V to 40V
COUT3
1µF
VOUT
60V MAX
L
10µH
D
CVIN
10µF
RVCC1
10
C3
15 LED String
RT8560A
R4
4, 5 SW
7 VCC1
CVCC1
1µF
R3
1k
5V
R1
VOUT
11 EN
12
LED4 15
OVP
RISET
RVCC2
10
6 VCC2
CVCC2
1µF
:
:
:
:
COUT1 COUT2
18
LED2 17
LED3 16
R2
VIN
LED1
:
:
:
:
:
:
:
:
:
:
:
:
RISET
5.36k
8
ILED = 20mA ×
5.36k
RISET
ACTL 9
C2
0.1µF
R5
1k
DCTL 10
PWM Signal
14 VC
13 SS
RVC
1.8k
GND
1, 2, 3, 19, 20, Exposed Pad (21)
C1
0.1µF
CVC
3.9nF
Figure 3. 1MHz, 20mA Full Scale Current PWM to Analog Dimming Control
VIN
4V to 40V
COUT3
1µF
VAVDD
6V to 40V
L
10µH
VOUT
60V MAX
D
CVIN
10µF
RVCC1
10
C2
15 LED String
RT8560A
R4
4, 5
5V
R3
1k
R1
VOUT
:
:
:
:
:
:
:
:
COUT1 COUT2
18
LED2 17
LED3 16
12
LED4 15
OVP
RISET
R2
VIN
LED1
11 EN
RVCC2
10
:
:
:
:
SW
7 VCC1
CVCC1
2.2µF
:
:
:
:
6 VCC2
CVCC2
1µF
8
ACTL 9
DCTL 10
RISET
5.36k
ILED = 20mA ×
5.36k
RISET
R5
1k
PWM Signal
14
RVC
1.8k
CVC
3.9nF
VC
13 SS
GND
1, 2, 3, 19, 20, Exposed Pad (21)
C1
0.1µF
Figure 4. Wide Range VIN Application by Connecting VCC1 to LCD Driver Power AVDD
DS8560A-01 April 2011
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3
RT8560A
Function Block Diagram
SW
OSC
-
VCC1
6.2V
+
2.5V
+
-
LED1
S
+
R
OVP
-
R
+
-
LED2
-
EN
2V
+
+
-
Shutdown
VCC2
VOUT
Regulation
Unit
VC
LED3
+
-
6uA
5V
SS
LED4
1.2V
DCTL
+
1.2V
200k
+
-
-
ACTL
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4
+
-
RISET
DS8560A-01 April 2011
RT8560A
Functional Pin Description
Pin Number
1, 2, 3, 19, 20,
21 (Exposed Pad)
4, 5
6
Pin Name
Pin Function
GND
Ground pin of the chip. The exposed pad must be soldered to a large PCB
and connected to GND for maximum power dissipation.
SW
PWM boost converter switch node.
VCC2
Bipolar power switch base current supply. Typical beta of the power NPN
switch is approximately 70. VCC2 can be connected either to VCC1 or to a
separate lower voltage, as low as 3V, for better system efficiency and/or
heat concern. A good bypass is necessary.
7
VCC1
Power supply of the chip. For good bypass, a low ESR capacitor is required.
8
RISET
A resistor or a current from DAC on this pin programs the full LED current.
9
ACTL
Analog/Digital dimming control. When using analog dimming,
5.36k
ILED = 20mA ×
for VACT L ≥ 1.2V.
RISET
By adding a 0.1uF filtering capacitor on ACTL pin, the PWM dimming signal
10
DCTL
on DCTL pin will be averaged out and converted into analog dimming signal
on ACTL pin.
11
EN
Chip enable pin, when low chip is in shutdown mode.
12
OVP
13
SS
Soft start pin, a capacitor of at least 10nF is required for soft start.
14
VC
PWM boost converter loop compensation node.
Channel 1 to Channel 4 LED current sink. Leave the pin unconnected if not
used.
Over voltage protection. PWM boost converter turns off when VOVP goes
higher than 2.5V.
18, 17, 16, 15
LED1, LED2,
LED3, LED4
DS8560A-01 April 2011
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5
RT8560A
Absolute Maximum Ratings
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(Note 1)
Supply Voltage, VCC1, VCC2 -----------------------------------------------------------------------------------------SW Pin Voltage at Switching Off -------------------------------------------------------------------------------------LED1, LED2, LED3, LED4 Pin ----------------------------------------------------------------------------------------EN Pin Voltage ------------------------------------------------------------------------------------------------------------RISET Pin Voltage -------------------------------------------------------------------------------------------------------ACTL, DCTL, OVP, SS, VC Pins Voltage --------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WQFN-20L 4x4 -----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WQFN-20L 4x4, θJA ------------------------------------------------------------------------------------------------------WQFN-20L 4x4, θJC -----------------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Mode) ---------------------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------------------
Recommended Operating Conditions
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42V
65V
25V
20V
4V
8V
1.852W
54°C/W
7°C/W
150°C
260°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Input Voltage, VCC1, VCC2 ---------------------------------------------------------------------------------- 6V to 40V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VCC1 = 17V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
VCC1 UVLO Threshold
VUVLO
VCC1 Rising
--
5.5
5.95
V
Supply Current
IVCC1
VC ≤ 0.4V (Switching off)
--
4
7
mA
Shutdown Current
ISHDN
V EN ≤ 0.7V
--
12
--
μA
Logic-High Voltage VEN_H
EN
Threshold Logic-Low Voltage VEN_L
2
--
5
--
--
0.8
Logic-High Voltage VACTL_H
ACTL
Threshold Logic-Low Voltage VACTL_L
2
--
5
--
--
0.15
EN Pin Input Current
V
V
IEN
V EN ≤ 5V
--
--
2
μA
ILED
2V > VLED > 0.7V, RISET = 5.36kΩ,
V ACTL >1.28V
19
20
21
mA
2V > VLED > 0.7V, RISET = 5.36kΩ,
V ACTL >1.28V, Calculating
(I(MAX) − I(MIN) / IAVERAGE x 100%)
--
--
3
%
LED Current Programming
LED Current
LED´s Current Matching
RISET Pin Voltage
VRISET
R ISET = 5.36kΩ, VACTL > 1.28V
--
1.21
--
V
Input Current of ACTL
IACTL
0.3V ≤ VACTL ≤ 1.2V
--
--
2
μA
To be continued
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DS8560A-01 April 2011
RT8560A
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Threshold of ACTL
VACTL
LED Current Off
--
0.2
--
V
Input Current of DCTL
IDCTL
0.3V ≤ V DCTL ≤ 6V
--
--
1
μA
Switching Frequency
840
1000
1160
kHz
Maximum Duty Cycle
--
88
--
%
Minimum On Time
--
200
--
ns
--
0.9
--
V
--
220
--
μA/V
PWM Boost Converter
Regulated VLED
Amplifier gm
Highest Voltage LED String
GM
Amplifier (gm) Output Current
2.4V > VC > 0.2V
--
±30
--
μA
VC Threshold
PWM Switch Off
--
0.7
--
V
SW On Voltage
ISW = 0.5A
--
0.4
--
V
1.2
1.5
--
A
--
2.5
--
V
SW Current Limit
ILIM
OVP & Soft Start
OVP Threshold
VOVP
OVP Input Current
IOVP
VOVP ≤ 2.5V
--
--
50
nA
Soft Start Current
ISS
VSS = 0V
--
7
--
μA
Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for
stress ratings. 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 for extended
periods may remain possibility to affect device reliability.
Note 2. θJA is measured in the natural convection at TA = 25°C on a high effective four layers thermal conductivity test board of
JEDEC 51-7 thermal measurement standard. The case point of θJC is on the expose pad for the WQFN package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
DS8560A-01 April 2011
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7
RT8560A
Typical Operating Characteristics
Efficiency vs. Input Voltage
LED Current vs. Input Voltage
100
26
90
24
60LEDs
LED Current (mA)
80
Efficiency (%)
70
60
50
40
30
20
22
20
LED1
LED2
LED3
LED4
18
16
14
12
10
0
10
8
12
16
20
24
28
32
36
40
8
12
16
24
1.24
23
1.22
22
28
32
36
40
1.20
V RISET (V)
LED Current (mA)
24
VRISET vs. Temperature
LED Current vs. Temperature
21
20
19
1.18
1.16
1.14
18
1.12
17
VIN = 12V
16
VIN = 12V
1.10
-40
-15
10
35
60
85
110
135
-40
1.24
18
1.23
16
LED Current (mA)
20
1.22
1.21
1.20
1.19
1.18
0
Input Voltage (V)
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8
100
120
6
1.15
28
80
32
36
40
ACTL = 200Hz
ACTL = 1kHz
ACTL = 10kHz
ACTL = 20kHz
ACTL = 30kHz
8
2
24
60
10
1.16
20
40
12
4
16
20
14
1.17
12
0
LED Current vs. ACTL PWM Duty Cycle
VRISET vs. Input Voltage
1.25
8
-20
Temperature (°C)
Temperature (°C)
V RISET (V)
20
Input Voltage (V)
Input Voltage (V)
ACTL = 0V to 3V, VIN = 12V
0%
0 10%
10 20%
20 30%
30 40%
40 50%
50 60%
60 70%
70 80%
80 90%
90 100
%
Duty Cycle (%)
DS8560A-01 April 2011
RT8560A
LED Current vs. ACTL Voltage
25
20
20
LED Current (mA)
LED Current (mA)
LED Current vs. DCTL PWM Duty Cycle
25
DCTL = 200Hz
DCTL = 1kHz
DCTL = 10kHz
15
10
15
10
5
5
VIN = 12V
DCTL = 0V to 3V, VIN = 12V
0
0
20
30
40
50
60
70
80
90
0
100
0.25
0.5
1
1.25
1.5
ACTL Voltage (V)
Duty Cycle (%)
Shutdown Current vs. Input Voltage
Frequency vs. Input Voltage
1.10
40
1.08
35
Shutdown Current (uA)
1.06
Frequency (MHz)
0.75
1.04
1.02
1.00
0.98
0.96
0.94
30
25
20
15
10
0.92
5
0.90
0
VEN = 0V
8
10
12
14
16
18
20
22
24
8
12
16
Input Voltage (V)
Switch Off Current vs. Input Voltage
24
28
32
36
40
SS Current vs. Temperature
5.0
10
4.9
9
4.8
8
4.7
7
SS Current (uA)
Switch Off Current (mA)
20
Input Voltage (V)
4.6
4.5
4.4
4.3
6
5
4
3
2
4.2
4.1
1
VC = 0V
VIN = 12V, CSS = 0.1uF
0
4.0
8
12
16
20
24
28
Input Voltage (V)
DS8560A-01 April 2011
32
36
40
-40
-20
0
20
40
60
80
100
120
Temperature (°C)
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9
RT8560A
OVP Voltage vs. Temperature
2.50
9
2.48
8
2.46
7
2.44
OVP Voltage (V)
SS Current (uA)
SS Current vs. Input Voltage
10
6
5
4
3
2
2.42
2.40
2.38
2.36
2.34
1
CSS = 0.1uF
0
2.32
VIN = 12V
2.30
8
12
16
20
24
28
32
36
40
-40
Input Voltage (V)
0
20
40
60
80
100
120
Temperature (°C)
OVP Voltage vs. Input Voltage
Limit Current vs. Input Voltage
2.8
2.5
2.7
2.0
Limit Current (A)
OVP Voltage (V)
-20
2.6
2.5
2.4
1.5
1.0
0.5
2.3
2.2
0.0
8
12
16
20
24
28
32
36
40
8
10 12 14 16 18 20
22 24 26 28 30 32
Input Voltage (V)
Input Voltage (V)
ACTL Voltage vs. Temperature
Power On from EN
0.40
ACTL Voltage (V)
0.35
VEN
(2V/Div)
0.30
0.25
0.20
VOUT
(20V/Div)
0.15
I IN
(500mADiv)
0.10
0.05
VIN = 12V
VIN = 12V, CSS = 0.1uF
0.00
-40
-20
0
20
40
60
80
100
120
Time (5ms/Div)
Temperature (°C)
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DS8560A-01 April 2011
RT8560A
Line Transient Response
OVP
VIN
(5V/Div)
VIN
(5V/Div)
VOUT
(20V/Div)
SW
(20V/Div)
IOUT
(50mA/Div)
VIN = 10.8V to 13.2V, RISET = 4.8kΩ
Time (50ms/Div)
DS8560A-01 April 2011
VIN = 12V, All LED Pin Open
Time (2.5ms/Div)
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11
RT8560A
Applications Information
The RT8560A is a current mode boost converter operated
at 1MHz to power up to 60 white LEDs with a
programmable current for uniform intensity. The part
integrates current sources, soft-start, and easy analog
and digital dimming control. The protection block provides
the circuitry for over-temperature, over-voltage and currentlimit protection features.
VIN
UVLO
PWM
EN
VIN must be turned
off early than EN and
PWM signal
Input UVLO
Power Sequence
Power-off
sequence
Abnormal Poweron sequence
VIN
UVLO
PWM
EN must be turned
on late than VIN
and PWM signal
Soft-Start
VOUT
No Soft-Start
If PWM turns
on late
VOUT
Figure 6. Power-On Sequence Control by VIN
EN and/or VIN should be
pulled low once PWM pull low
for over 10ms
EN/VIN
PWM
Please refer to the below Figure 5 and 7. The
recommended power-on sequence is that the PWM ready
before EN and/or VIN ready. If not, the Soft-Start function
will be disabled. As to power-off sequence, the EN/VIN
must be pulled low within 10ms to prevent “Hard-Start”
shown as Figure 7.
EN
VIN must be
turned on late
than EN and
PWM signal
Soft-Start
The input operating voltage range of the RT8560A is 6V to
40V. An input capacitor at the VCC1 and VCC2 pin can
reduce ripple voltage. It is recommended to use a ceramic
10uF or larger capacitance as the input capacitor. This IC
provides an under voltage lockout (UVLO) function to
enhance the stability when startup. The UVLO threshold
of input rising voltage is around 5.5V.
Power-on
sequence
Abnormal Poweron sequence
Power-off
sequence
Power-on
sequence
EN must be turned
off early than VIN
and PWM signal
10ms
Figure 7. To Prevent “Hard-Start” Sequence
Soft Start
The RT8560A employs a soft start feature to limit the inrush
current. The soft-start circuit prevents the excessive inrush
current and input voltage droop. The soft-start time is
determined by capacitor CSS connected to SS with a 7uA
constant current to charge CSS. The value of capacitor
CSS is user-defined to satisfy designer' requirement.
LED connection
No Soft-Start
If PWM turns
on late
Figure 5. Power-On Sequence Control by EN
The RT8560A equips 4 channel LED divers and each
channel supports up to 15 LEDs. The 4 LED strings are
connected from VOUT to pin 15, 16, 17 and 18
respectively. If one of the LED channel is not used, the
LED pin should be opened directly.
Setting and Regulation of LED current
The LED current can be calculated by the following
equation :
ILED = 20mA × 5.36k
RISET
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12
DS8560A-01 April 2011
RT8560A
Where,
Over Voltage Protection
VRISET is the voltage of the RISET pin (1.21V typ.) and the
RISET is the resister between RISET pin and GND.
The RT8560A equips over voltage protection (OVP)
function. When the voltage at OVP pin reaches a threshold
of approximately 2.5V, the MOSFET drive output (SW)
will turn “OFF”. The MOSFET drive output (SW) will turn
“ON” again once the voltage at OVP drops below the
threshold of approximately 2.5V.
This setting is the reference for the LED current at LED14 and represents the sensed LED current for each string.
The DC/DC converter regulates the LED current according
to the setting.
So, the output voltage can be clamped at a certain voltage
level and it can be calculated by the following equation :
Brightness Control
The RT8560A features both analog and digital dimming
control. Analog dimming is linearly controlled by an
external voltage (0.3V < VACTL < 1.2V). With an on-chip
output clamping amplifier and a 200kΩ resistor, PWM
dimming signal is easily low-pass filtered to an analog
dimming signal with one external capacitor for noise-free
PWM dimming. A very high contrast ratio true digital PWM
dimming can be achieved by driving ACTL pin with a PWM
signal and suggest PWM frequency is from 200Hz to
10kHz. Refer to Figure 8, the minimum dimming duty can
be as low as 1% for the frequency range from 100Hz to
300Hz. For the dimming frequency from 300Hz to 1kHz,
the duty is about 5%. If the frequency is increased to
1kHz to 30kHz, the duty will be about 10%.
LED Current vs. ACTL PWM Duty Cycle
20
18
LED Current (mA)
16
VOUT, OVP = 2.5 × ⎛⎜ 1+ R1 ⎞⎟
⎝ R2 ⎠
Where,
R1 and R2 are the voltage divider connected to OVP pin.
If at least one string is in normal operation, the controller
will automatically ignore the open strings and continue to
regulate the current for the string(s) in normal operation.
Current-limit Protection
The RT8560A can limit the peak current to achieve over
current protection. The RT8560A senses the inductor
current of on period that flows through SW pin. The duty
cycle depend on current signal and internal slope
compensation compared with error signal. The internal
N-MOSFET will be turned off when the current signal is
large than internal slope compensation. In the off period,
the inductor current will be descended until the internal
N-MOSFET is on by the oscillator.
14
ACTL = 200Hz
ACTL = 1kHz
ACTL = 10kHz
ACTL = 20kHz
ACTL = 30kHz
12
10
8
6
4
2
ACTL = 0V to 3V, VIN = 12V
0
0%
0 10%
10 20%
20 30%
30 40%
40 50%
50 60%
60 70%
70 80%
80 90%
90 100
%
Duty Cycle (%)
Figure 8. LED Current vs. PWM Dimming Duty Cycle
Over Temperature Protection
The RT8560A has over temperature protection (OTP)
function to prevent the excessive power dissipation from
overheating. OTP will shut down the IC while junction
temperature exceeds 150°C. Main converter starts
switching once the junction temperature is cooled
approximately 20°C.
Inductor Selection
The value of the output inductor (L), where the transition
from discontinuous to continuous mode occurs is
approximated by the following equation :
L=
DS8560A-01 April 2011
(VOUT − VIN ) × VIN2
2 × IOUT × f × VOUT 2
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13
RT8560A
Where,
Layout Guideline
VOUT = maximum output voltage.
PCB layout is very important for designing power switching
converter circuits. Some recommended layout guides that
should be strictly be followed are shown as follows :
Place L and D connected to SW pin as close as possible.
The trace should be short and wide as possible.
`
It is recommended to place CVcc1 and CVcc2 close to
VCC1 and VCC2 pins.
`
Pin14 is the compensation point to adjust system
stability. Place the compensation components to pin14
as close as possible, no matter the compensation is
RC or capacitance.
Schottky diode is a good choice for an asynchronous
Boost converter due to the small forward voltage. However,
power dissipation, reverse voltage rating and pulsating peak
current are the important parameters for Schottky diode
selection. Choose a suitable diode whose reverse voltage
rating is greater than the maximum output voltage.
Capacitor Selection
The input capacitor reduces current spikes from the input
supply and minimizes noise injection to the converter. For
most applications, a 10uF ceramic capacitor is sufficient.
A value higher or lower may be used depending on the
noise level from the input supply and the input current to
the converter.
Place these components
as close as possible.
C OUT1
C OUT2
D
V OUT
17
16
1
15
GND
GND
SW
SW
2
14
GND
3
13
12
4
21
5
L
C OUT3
20 19 18
GND
C VIN
6
7
8
9
11
10
DCTL
Diode Selection
ACTL
η is the efficiency of the power converter.
RISET
Where,
GND
The inductor must be selected with a saturated current
rating that is greater than the peak current provided by
the following equation :
IPEAK = VOUT × IOUT + VIN × T ⎛⎜ VOUT − VIN ⎞⎟
η × VIN
2 × L × ⎝ VOUT
⎠
LED3
`
GND
The boost converter operates in discontinuous mode over
the entire input voltage range when the L1 inductor value
is less than this value L. With an inductance greater than
L, the converter operates in continuous mode at the
minimum input voltage and may be discontinuous at higher
voltages.
LED2
The power components L, D, CVIN, COUT1 and COUT2
must be placed as close as possible to reduce the ac
current loop. The PCB trace between power components
must be as short and wide as possible due to large
current stream flows through these traces during
operation.
LED1
`
IOUT = sum of current from all LED strings.
VCC2
f = operating frequency.
VCC1
VIN = minimum input voltage.
LED4
C VC1
R VC
VC
GND
SS
OVP
C VC2
Locate the compensation
EN
components to VC pin as
close as possible.
GND
V IN
C VCC2
R VCC2
R VCC1
GND
C VCC1
Locate the C VCC1 and C VCC2 as
close as possible to V CC1 and
V CC2 pin.
Figure 9. PCB Layout Guide
It is recommended to choose a ceramic capacitor bases
on the output voltage ripple requirements. The minimum
value of the output capacitor COUT is approximately given
by the following equation :
COUT =
(VOUT − VIN ) × IOUT
η × VRIPPLE × VOUT × f
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14
DS8560A-01 April 2011
RT8560A
Outline Dimension
1
1
2
2
DETAIL A
Pin #1 ID and Tie Bar Mark Options
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.150
0.300
0.006
0.012
D
3.950
4.050
0.156
0.159
D2
2.650
2.750
0.104
0.108
E
3.950
4.050
0.156
0.159
E2
2.650
2.750
0.104
0.108
e
L
0.500
0.350
0.020
0.450
0.014
0.018
W-Type 20L QFN 4x4 Package
Richtek Technology Corporation
Richtek Technology Corporation
Headquarter
Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City
5F, No. 95, Minchiuan Road, Hsintien City
Hsinchu, Taiwan, R.O.C.
Taipei County, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Tel: (8862)86672399 Fax: (8862)86672377
Email: [email protected]
Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit
design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be
guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.
DS8560A-01 April 2011
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15