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PDF RT8562 Data sheet ( Hoja de datos )
| Número de pieza | RT8562 | |
| Descripción | High Voltage 8 Channel LED Driver | |
| Fabricantes | Richtek | |
| Logotipo |  |
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RT8562
High Voltage 8 Channel LED Driver
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
VIN 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 RT8562 automati-
cally detects and disconnects any unconnected and/or
broken strings during operation from PWM loop to prevent
VOUT 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 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.
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)
Note :
Lead Plating System
G : Green (Halogen Free and Pb Free)
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.
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
DS8562-01 April 2011
Features
z High Voltage : VIN up to 24V, VOUT up to 40V, Driving
up to 80 x 3.6V LEDs (10 each channel)
z Channel Current Programmabe 10mA to 30mA and
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 VIN Under Voltage Lockout
z Over Temperature Protection
z Current Limiting Protection
z Small 24-Lead WQFN Package
z RoHS Compliant and Halogen Free
Applications
z UMPC and Notebook Computer Backlight
z GPS, Portable DVD Backlight
z Desk Lights and Room Lighting
Pin Configurations
(TOP VIEW)
24 23 22 21 20 19
EN 1
18 PGND2
NC 2
17 PGND1
SS
NC
GND
PWM
3
4
5
6
GND
16 OVP
15 CH1
14 CH2
25 13 CH3
7 8 9 10 11 12
WQFN-24L 4x4
www.richtek.com
1
1 page  
RT8562
Electrical Characteristics
(VIN = 17V, TA = 25°C, unless otherwise specified)
Parameter
Supply Current
VIN Under Voltage Lockout
Threshold
Shutdown Current
EN Pin Input Current
EN Logic Input
High Level
Low Level
PWM Logic Input
High Level
Low Level
LED Current Programming
LED Current
LEDs Current Matching
ISET Pin Voltage
Input Current of PWM
Threshold of PWM
VCHx Threshold
Symbol
Test Conditions
IVIN
VUVLO
ISHDN
IEN
VEN_H
VEN_L
VPWM_H
VPWM_L
COMP ≤ 0.2V (Switching off)
VIN Rising
VIN Falling
VEN ≤ 0.7V
VEN ≤ 5V
Min Typ Max Unit
-- 3 5 mA
--
5.6 5.95
V
-- 4.9 --
-- -- 10 μA
-- -- 0.1 μA
1.6 --
-- --
5
1
V
1.3
--
--
--
5
0.15
V
ICHx
2V > VCHx > 0.6V, RISET = 4.75kΩ,
VPWM > 1.2V
19 20 21 mA
2V > VCHx > 0.6V, RISET = 4.75kΩ,
VPWM > 1.2V, Calculating
-- -- 1.5 %
(I(MAX) − I(MIN)) / IAverage x 100%
VISET 3.6kΩ ≤ RISET ≤ 9.6kΩ, VPWM > 1.2V 1.17 1.2 1.23 V
IPWM
0.3V ≤ VPW M ≤ 1.2V
-- 1 2 μA
VPWM LED Current Off
-- 0.2 --
V
Un-connection
-- 0.1 --
V
PWM Boost Converter
Switching Frequency
Minimum On Time
Regulated VCHx
Amplifier (gm) Output Current
COMP Threshold
LX1, LX2 RDS(ON)
LX1, LX2 Current Limit
SW Maximum Duty
ILIM
Highest Voltage LED String
2.4V > COMP > 0.2V
PWM Switch Off
0.8 1 1.2 MHz
-- 100 --
ns
0.5 0.6 0.7
V
-- ±15 --
μA
0.1 0.2 --
V
-- 0.3 0.5 Ω
2.5 -- -- A
-- 88 -- %
OVP & Soft Start
OVP Threshold
OVP Input Current
Soft Start Current
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
VOVP
IOVP
ISS
TSD
VOVP ≤ 3V
VSS ≤ 2.5V
1.1 1.2 1.3
-- -- 50
358
-- 150 --
-- 20 --
V
nA
μA
°C
°C
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.
DS8562-01 April 2011
www.richtek.com
5
5 Page 
RT8562
Where,
VOUT = maximum output voltage.
VIN = minimum input voltage.
f = operating frequency.
IOUT = sum of current from all LED strings.
η is the efficiency of the power converter.
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.
The inductor must be selected with a saturation current
rating greater than the peak current provided by the
following equation :
IPEAK
=
VOUT ×IOUT
η × VIN
+
VIN × T
2×L
⎛⎜⎝
VOUT − VIN
VOUT
⎞⎟⎠
Diode Selection
Schottky diode is a good choice for an asynchronous
Boost converter due to the small forward voltage. However,
for power dissipation, reverse voltage rating and pulsating
peak current are the important parameters of Schottky
diode consideration. 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.
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
Layout Guideline
PCB layout is very important to design power switching
converter circuits. The following layout guide lines should
be strictly followed for best performance of the RT8562.
` The power components L, D1, C1, COUT1 and COUT2 must
be placed as close as possible to reduce the ac current
loop. The PCB trace between power components must
be short and wide as possible due to large current flow
through these trace during operation.
` Place L and D1 connected to LX pin as close as possible.
The trace should be short and wide as possible.
` It is recommend to place C6 close to VIN pin.
` Pin22 is the compensation point to adjust system
stability. Place the compensation components to pin22
as close as possible.
Locate the compensation
VIN
components to COMP
Place power components
pin as close as possible.
C2 as close as possible.
R4 R1
C6
CVC2
L
C1
D1
GND
COUT1
COUT2
Locate the CVIN2 as
VOUT
close to VIN pin as
possible.
24 23 22 21 20 19
EN 1
18 PGND2
NC 2
17 PGND1
SS 3
NC 4
GND
16 OVP
15 CH1
GND 5
PWM 6
14 CH2
25 13 CH3
7 8 9 10 11 12
Figure 8
DS8562-01 April 2011
www.richtek.com
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet RT8562.PDF ] | |
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