®
RT8561A
High Voltage 8-CH LED Driver
General Description
The RT8561A is a 40V 8-CH LED driver capable of delivering
30mA to each channel with 10 LEDs (3.6V per diode),
total of 80 LEDs with one driver. The RT8561A is a current
mode boost converter operated at 1MHz, wide V
IN
range
covers from 6V to 24V and the on-chip current switch is
rated at 2.5A.
The PWM output voltage loop regulates the LED pins to
0.6V with an auto-adjustment circuit allowing voltage
mismatches between LED strings. The RT8561A automati-
cally detects and disconnects any unconnected and/or
broken strings during operation from PWM loop to prevent
V
OUT
from over voltage.
The 1.5% 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 the RT8561A. Analog dimming is linearly
controlled by an external voltage. With an on-chip output
clamping amplifier and a 300kΩ 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.
Other protecting features include programmable output
over voltage protection, LED current limit, PWM switch
current limit and thermal shutdown.
The RT8561A is packaged with a tiny footprint package of
WQFN-24L 4x4 packages.
Features
High Voltage : V
IN
up to 24V, V
OUT
up to 40V, Driving
up to 80 x 3.6V LEDs (10 each channel)
Channel Current Programmable 10mA to 30mA and
Matched to 1.5%
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 Shutdown
Providing High Accuracy Digital Dimming by PWM
at ACTL Pin
V
IN
Under Voltage Lockout
Over Temperature Protection
Current Limiting Protection
Small 24-Lead WQFN Package
RoHS Compliant and Halogen Free
Applications
UMPC and Notebook Computer Backlight
GPS, Portable DVD Backlight
Desk Lights and Room Lighting
Pin Configurations
(TOP VIEW)
GND
GND
GND
GND
SW
20
24
23
22
21
LED1
LED2
LED3
LED4
LED5
OVP
SW
19
18
17
1
2
3
4
5
6
7
8
9
10
11
25
12
VCC
CREG
LED8
LED7
LED6
EN
GND
16
15
14
13
Ordering Information
RT8561A
Package Type
QW : WQFN-24L 4x4 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
RISET
ACTL
WQFN-24L 4x4
Note :
Richtek products are :
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
Marking Information
CZ= : Product Code
CZ=YM
DNN
YMDNN : Date Code
is a registered trademark of Richtek Technology Corporation.
DS8561A-02 April 2012
DCTL
VC
NC
SS
www.richtek.com
1
RT8561A
Typical Application Circuit
V
IN
6V to 24V
L
10µH
C
VIN1
10µF
19, 20 SW
18
C
VIN1
2.2µF
V
OUT
5V
R1
R2
17
4.7µF
0.1µF
R
VC
1.8k
C
VC
3.9nF
CREG
1k
VCC
V
OUT
40V MAX
D
C
OUT
10µF
RT8561A
LED1 1
2
LED2
:
:
:
:
:
:
:
:
R
VIN1
10
...
::
:
:
:
: 10 LED String
:
:
13 EN
6
OVP
LED7
15
.
.
.
R
ISET
4.75k
LED8 16
RISET
10
I
LED
(mA) = 20 x 4.75
R
ISET
(kΩ)
9 SS
7
VC
12
DCTL
GND
ACTL
21, 22, 23, 24, 25 (Exposed Pad)
11
1k
PWM Signal
Figure 1. 1MHz, 20mA Full Scale Current PWM Dimming Control
V
IN
6V to 24V
V
OUT
40V MAX
D
C
OUT
10µF
RT8561A
19, 20 SW
18
C
VIN1
2.2uF
V
OUT
5V
R1
R2
17 CREG
4.7µF
0.1µF
R
VC
1.8k
C
VC
3.9nF
9 SS
7
VC
12
DCTL
GND
ACTL
1k
VCC
LED1 1
2
LED2
:
:
:
:
:
:
:
:
L
10µH
C
VIN1
10µF
R
VIN1
10
...
::
:
:
:
: 10 LED String
:
:
13 EN
6
OVP
LED7
15
.
.
.
R
ISET
4.75k
LED8 16
RISET
10
I
LED
(mA) = 20 x 4.75
R
ISET
(kΩ)
21, 22, 23, 24, 25 (Exposed Pad)
11
1k
Analog
Dimming
DCTL can be floating or
connected to ACTL
Figure 2. 1MHz, 20mA Full Scale Current Analog Dimming Control
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS8561A-02 April 2012
RT8561A
V
IN
6V to 24V
L
10µH
C
VIN1
10µF
19, 20 SW
18
C
VIN1
2.2µF
V
OUT
5V
R1
R2
17
4.7µF
0.1µF
R
VC
1.8k
C
VC
3.9nF
PWM Signal
CREG
1k
VCC
V
OUT
40V MAX
D
C
OUT
10µF
RT8561A
LED1 1
2
LED2
:
:
:
:
:
:
:
:
R
VIN1
10
...
::
:
:
:
: 10 LED String
:
:
13 EN
6
OVP
LED7
15
.
.
.
R
ISET
4.75k
LED8 16
RISET
10
I
LED
(mA) = 20 x 4.75
R
ISET
(kΩ)
9 SS
7
1k 12
VC
DCTL
GND
ACTL
21, 22, 23, 24, 25 (Exposed Pad)
11
0.1µF
Figure 3. 1MHz, 20mA Full Scale Current PWM to Analog Dimming Control
V
IN
4V to 36V
L
10µH
V
AVDD
6V to 24V
R
VIN1
10
C
VIN1
2.2µF
C
VIN1
10µF
19, 20 SW
18
5V
R1
R2
17
4.7µF
0.1µF
R
VC
1.8k
C
VC
3.9nF
1k
VCC
D
C
OUT
10µF
RT8561A
LED1 1
2
LED2
:
:
:
:
:
:
:
:
V
OUT
40V MAX
...
::
:
:
:
: 10 LED String
:
:
13 EN
6
OVP
LED7
15
V
OUT
.
.
.
R
ISET
4.75k
LED8 16
CREG
RISET
10
I
LED
(mA) = 20 x 4.75
R
ISET
(kΩ)
9 SS
7
12
VC
DCTL
GND
ACTL
21, 22, 23, 24, 25 (Exposed Pad)
11
PWM Signal
Note :
1. Due to the limitation of maximum duty 5V input can support typically to V
OUT
= 33V.
2. Due to the limitation of maximum duty 4V input can support typically to V
OUT
= 26V.
Figure 4. Wide Range VIN Application by Connecting VCC Pin to LCD Driver Power AVDD
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8561A-02 April 2012
www.richtek.com
3
RT8561A
Functional Pin Description
Pin No.
1, 2, 3, 4, 5
6
7
8
9
10
11
Pin Name
LED1, LED2,
LED3, LED4,
LED5
OVP
VC
NC
SS
RISET
ACTL
Pin Function
Channel 1 to Channel 5 LED current sink. Leave the pin unconnected if not
used.
Over Voltage Protection. PWM boost converter turns off when V
OVP
goes
higher than 1.2V.
PWM boost converter loop compensation node.
No Internal Connection.
Soft Start Pin, a capacitor of at least 10nF is required for soft start.
A resistor or a current from DAC on this pin programs the full LED current.
Analog/Digital dimming control. When using analog dimming,
20 x 4.75
I
LED
(mA) =
for V
ACTL
≥
1.2V.
R
ISET
(kΩ)
By adding a 0.1μF filtering capacitor on the ACTL pin, the PWM dimming
signal on the DCTL pin will be averaged out and converted into analog
dimming signal on the ACTL pin.
Chip enable pin, when pulled low, chip is in shutdown mode.
Channel 6 to Channel 8 LED current sink. Leave the pin unconnected if not
used.
1μF capacitor should be placed on this pin to stabilize the 5V output of the
internal regulator. This regulator is for chip internal use only.
Power supply of the chip. For good bypass, a low ESR capacitor is required.
PWM boost converter switch node.
Ground pin of the chip. The exposed pad must be soldered to a large PCB
and connected to GND for maximum power dissipation.
12
13
14, 15, 16
17
18
19, 20
21, 22, 23, 24,
25 (Exposed Pad)
DCTL
EN
LED6, LED7,
LED8
CREG
VCC
SW
GND
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8561A-02 April 2012
www.richtek.com
5
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