Richtek RT8562GQW Schematic [ru]
High Voltage 8 Channel LED Driver
RT8562
General Description
The RT8562 is a 40V 8-channel LED driver capable of
delivering 30mA to each channel with 10 LEDs (3.6V per
diode), total of 80 LEDs with one driver. The RT8562 is a
current mode boost converter opearated at 1MHz, wide
V
range covers from 6V to 24V and the on-chip current
IN
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 RT8562 automati-
cally detects and disconnects any unconnected and/or
broken strings during operation from PWM loop to prevent
V
from over voltage.
OUT
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 RT8562. Analog dimming is linearly
controlled by an external voltage. A very high contrast ratio
true digital PWM dimming can be achieved by driving PWM
pin with a PWM signal.
Features
z High V oltage : V
up to 80 x 3.6V LEDs (10 each channel)
z Channel Current Progra mma be 10mA to 30mA a nd
Matched to 1.5%
z Current Mode PWM 1MHz Boost Converter
z Easy Analog and Digital Dimming Control
z Programmable Soft Start
z Automatic Detecting Unconnected and/or Broken
Channel
z Programmable Over Voltage Protection
z Disconnects LED in Shutdown
z Providing High Accuracy Digital Dimming by PWM
Signal
z V
Under Voltage Lockout
IN
zz
z Over Temperature Protection
zz
zz
z Current Limiting Protection
zz
zz
z Small 24-Lead WQFN Package
zz
zz
z RoHS Compliant and Halogen Free
zz
up to 24V , V
IN
up to 40V , Driving
OUT
Applications
Other protecting features include programmable output
over voltage protection, LED curren limit, PWM switch
current limit and thermal shutdown.
The RT8562 is packaged with a tiny footprint package of
WQFN-24L 4x4 packages.
Ordering Information
RT8562
Package Type
QW : WQFN-24L 4x4 (W-Type)
Lead Plating System
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.
G : Green (Halogen Free and Pb Free)
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
z UMPC and Notebook Computer Backlight
z GPS, Portable DVD Backlight
z Desk Lights and Room Lighting
Pin Configurations
(TOP VIEW)
CH5 NC
LX1
LX2
18
17
16
15
14
25
13
11
CH4
ISET
EN
NC
SS
NC
GND
PWM
VDC
VIN
24 2223
1
2
3
4
5
6
7
8 9 10 12
CH8
CH7
WQFN-24L 4x4
COMP
21 20 19
GND
CH6
PGND2
PGND1
OVP
CH1
CH2
CH3
DS8562-01 April 2011 www.richtek.com
1
RT8562
Typical Application Circuit
V
IN
6V to 24V
PWM Signal
R1
1.8k
C2
3.9nF
C3
4.7µF
10
R6
R4
1µF
C6
1k
C4
0.1µF
C1
10µF
R5
1k
23
1
6
22
24
3
L
10µH
RT8562
VIN
EN5V
PWM
COMP
VDC
SS
GND
5, Exposed Pad (25)
OVP
ISET
LX1
LX2
CH1
CH2
CH7
CH8
19
20
15
14
8
7
16
11
I
LED
D1
R7
R
ISET
4.75k
(mA) =
C7
...
C5
10µF
:
:
:
:
R2
R3
20 x 4.75
Ω)
R(k
ISET
V
OUT
40V MAX
:
:
...
:
:
:
:
:
:
V
OUT
:
10 LED String
:
:
:
V
6V to 24V
Analog
Dimming
R1
1.8k
C2
3.9nF
Figure 1. 1MHz, 20mA Full Scale Current PWM Dimming Control
IN
C3
4.7µF
R6
R4
10
C6
1µF
1k
R5
1k
C4
0.1µF
C1
10µF
10µH
RT8562
23
VIN
1
EN5V
6
PWM
22
COMP
24
VDC
3
SS
GND
5, Exposed Pad (25)
L
19
LX1
20
LX2
15
CH1
14
CH2
8
CH7
7
CH8
16
OVP
11
ISET
I
LED
D1
R7
...
R
ISET
4.75k
(mA) =
C5
10µF
C7
20 x 4.75
R(k
R3
ISET
R2
Ω)
:
:
:
:
Figure 2. 1MHz, 20mA Full Scale Current Analog Dimming Control
V
OUT
40V MAX
:
:
...
:
:
:
:
:
:
V
OUT
:
10 LED String
:
:
:
DS8562-01 April 2011www.richtek.com
2
V
4V to 36V
V
AVDD
6V to 24V
Analog
Dimming
R1
1.8k
C2
3.9nF
L
IN
C7
C1
1µF
10µF
R4
R5
R6
C3
4.7µF
10
1k
1k
C6
2.2µF
C4
0.1µF
23
1
6
22
24
3
10µH
RT8562
VIN
EN5V
PWM
COMP
VDC
SS
GND
5, Exposed Pad (25)
LX1
LX2
CH1
CH2
CH7
CH8
OVP
ISET
19
20
15
14
8
7
16
11
I
LED
D1
R7
R
ISET
4.75k
(mA) =
Note :
1. Due to the limitaion of maximum duty, 5V input can support typically to V
2. Due to the limitaion of maximum duty, 4V input can support typically to V
C8
...
OUT
OUT
C5
10µF
:
:
:
:
R2
R3
20 x 4.75
Ω)
R(k
ISET
= 33V.
= 26V.
V
OUT
40V MAX
:
:
...
:
:
:
:
:
:
V
OUT
:
10 LED String
:
:
:
RT8562
Figure 3. Wide Range VIN Application by Connecting VCC Pin to LCD Driver Power AVDD
Function Block Diagram
VIN
5.6V
OVP
1.2V
EN
1.6V
VDC
COMP
SS
5V
LDO
5uA
+
+
-
+
Shutdown
OSC
S
R
R
+
-
V
OUT
Regulation
Unit
LX1, LX2
5V
+
-
+
-
CH1
CH2
.
.
.
+
-
CH7
CH8
PWM
+
-
ISET
+
-
DS8562-01 April 2011 www.richtek.com
3
RT8562
Functional Pin Description
Pin No. Pin Name Pin Function
1 EN Chip enable pin, when pulled low, chip is in shutdown mode.
2, 4, 21 NC No Internal Connection.
3 SS Soft Start Pin, a capacitor of at least 10nF is required for soft start.
5,
25 (Exposed Pad)
GND
6 PWM
11 ISET A resistor or a current from DAC on this pin programs the full LED current.
10, 9, 8, 7 CH5 to CH8 Channel 5 to Channel 8 LED current sink. Leave the pin unconnected if not used.
15, 14, 13, 12 CH1 to CH4 Channel 1 to Channel 4 LED current sink. Leave the pin unconnected if not used.
16 OVP
17, 18
PGND1,
PGND2
19, 20 LX1, LX2 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.
Analog/Digital dimming control. When using analog dimming,
I (mA) = for V 1.2V.
LED PW M
Over Voltage Protection. PWM boost converter turns off when V
20 x 4.75
R(kΩ)
ISET
≥
OVP
higher than 1.2V.
Power Ground (LX1/LX2 power return).
goes
22 COMP PWM boost converter loop compensation node.
23 VIN Power supply of the chip. For good bypass, a low ESR capacitor is required.
24 VDC
Put 1μF capacitor on this pin to stabilize the 5V output of the internal regulator.
This regulator is for chip internal use only.
Absolute Maximum Ratings (Note 1)
z Supply Voltage, VIN ------------------------------------------------------------------------------------------------------ 28V
z LX1, LX2 Pin Voltage at Switching Off -------------------------------------------------------------------------------- 45V
z CH1 to CH8 Pin ------------------------------------------------------------------------------------------------------------ 35V
z PWM, EN, OVP Pin Voltage ------------------------------------------------------------------------------------------- −0.3V to 5.5V
z Power Dissipation, P
WQFN-24L 4x4 ------------------------------------------------------------------------------------------------------------ 1.923W
z Package Thermal Resistance (Note 2)
WQFN-24L 4x4, θJA------------------------------------------------------------------------------------------------------- 52°C/W
WQFN-24L 4x4, θJC------------------------------------------------------------------------------------------------------ 7°C/W
z Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C
z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------- 260°C
z Storage Temperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Mode) ---------------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ------------------------------------------------------------------------------------------------------ 200V
@ TA = 25°C
D
Recommended Operating Conditions (Note 4)
z Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 6V to 24V
z Junction Temperature Range --------------------------------------------------------------------------------------------
z Ambient Temperature Range --------------------------------------------------------------------------------------------
4
−40°C to 125°C
−40°C to 85°C
DS8562-01 April 2011www.richtek.com
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