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PDF RT8482 Data sheet ( Hoja de datos )
| Número de pieza | RT8482 | |
| Descripción | High Voltage High Current LED Driver Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT8482
High Voltage High Current LED Driver Controller for Buck
Boost, or Buck-Boost Topology
General Description
The RT8482 is a current mode PWM controller designed
to drive an external MOSFET for high current LED
applications. With a current sense amplifier threshold of
190mV, the LED current is programmable with one
external current sense resistor. With a maximum
operating input voltage of 36V and output voltage up to
48V, the RT8482 is ideal for Buck, Boost or Buck-Boost
operation.
With 350kHz operating frequency, the external inductor
and capacitors can be small while maintaining high
efficiency.
Dimming can be either analog or PWM digital. The unique
built-in clamping comparator and filter allow easy low
noise analog dimming conversion from PWM signal with
only one external capacitor.
The RT8482 is available in WQFN-16L 3x3 and
SOP-16 packages.
Features
z High Voltage Capability : VIN Up to 36V, VOUT Up to
48V
z Buck, Boost or Buck-Boost Operation
z Current Mode PWM with 350kHz Switching
Frequency
z Easy Dimming : Analog, PWM Digital or PWM
Converting to Analog with One External Capacitor
z Programmable Soft Start to Avoid Inrush Current
z Programmable Over Voltage Protection
z VIN Under Voltage Lockout and Thermal Shutdown
z 16-Lead WQFN and SOP Packages
z RoHS Compliant and Halogen Free
Applications
z General Industrial High Power LED Lighting
z Desk Lights and Room Lighting
z Building and Street Lighting
z Industrial Display Backlight
Ordering Information
RT8482
Package Type
S : SOP-16
QW : WQFN-16L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
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.
Marking Information
RT8482GS
RT8482
GSYMDNN
RT8482GS : Product Number
YMDNN : Date Code
RT8482GQW
H9=YM
DNN
H9= : Product Code
YMDNN : Date Code
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8482-02 May 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
Function Block Diagram
RT8482
EN
VCC
OVP
VC
SS
DCTL
2V
4.5V
1.18V
8.5V +
+ Shutdown
-
-
-
OSC
S
+
R
+R
- RR
-
+
VOC
5V
100k
110mV
6µA
1.2V
+
-
-
GM
+
1.2V
+
-
GBIAS
GATE
ISW
ISN
ISP
GND
ACTL
VISP – VISN
(mV)
190
0 0.2
1.2
Figure 4
VACTL (V)
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8482-02 May 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
be set by the following equation :
RT8482
LED load, or with a resistive voltage divider to VIN to reduce
output power and switching current when VIN is low. The
presence of a time varying differential voltage signal (ripple)
across ISP and ISN at the switching frequency is expected.
The amplitude of this signal is increased by high LED load
current, low switching frequency and/or a smaller value
output filter capacitor. The compensation capacitor on the
VC pin filters the signal so the average difference between
ISP and ISN is regulated on the user-programmed value.
Dimming Control
For LED applications where a wide dimming range is
required, two competing methods are available: analog
dimming and PWM dimming. The easiest method is to
simply vary the DC current through the LED by analog
dimming.
However, the better dimming method is PWM dimming,
which switches the LED on and off by different duty cycle
to control the average LED current. The PWM dimming
offers several advantages over analog dimming and is much
preferred by LED manufacturers. One advantage is the
chromatic ity of the LEDs which remains unchanged in
this scheme since the LED current is either zero or at
programmed current. Another advantage of PWM dimming
over analog dimming is that a wider dimming range is
possible.
The RT8482 features both analog and digital dimming
control. Analog dimming is linearly controlled by an
external voltage (0.2V < VACTL < 1.2V). With an on-chip
output clamping amplifier and a resistor. PWM dimming
signal fed at the DCTL pin can be easily low-pass filtered
to an analog dimming signal with one external capacitor
from the ACTL pin to GND for noise-free PWM dimming. A
very high contrast ratio true digital PWM dimming can be
achieved by driving the ACTL pin with a PWM signal from
100Hz to10kHz.
Output Over Voltage Setting
The RT8482 is equipped with an Over Voltage Protection
(OVP) function. When the voltage at the OVP pin exceeds
a threshold of approximately 1.18V, the power switch is
turned off. The power switch can be turned on again once
the voltage at the OVP pin drops below 1.18V. For Boost
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8482-02 May 2012
and Buck-Boost applications, the output voltage can be
set by the following equation :
VOUT,
OVP
= 1.18 × ⎛⎜⎝1+
R1 ⎞
R2 ⎟⎠
where,
R1 and R2 are the voltage divider resistors from VOUT to
GND with the divider center node connected to the OVP
pin.
ISW Sense Resistor Selection
The resistor, RSW, between the source of the external
N-MOSFET and GND should be selected to provide
adequate switch current to drive the application without
exceeding the 110mV (typical) current limit threshold on
the ISW pin of the RT8482. For real applications, select a
resistor that gives a switch current at least 30% greater
than the required LED current.
For Buck application, select a resistor according to :
RSW, Buck
=
⎛
⎜⎝
0.08V
IOUT
⎞
⎟⎠
For Buck-Boost application, select a resistor according
to :
RSW, Buck-Boost
=
⎛ VIN × 0.08V
⎜
⎝
(VIN
+
VOUT
)
×
IOUT
⎞
⎟
⎠
For Boost application, select a resistor according to :
RSW, Boost
=
⎛ VIN × 0.08V
⎜⎝ VOUT × IOUT
⎞
⎟⎠
The placement of RSW should be close to the source of
the N-MOSFET and GND of the RT8482. The ISW pin
input to the RT8482 should be a Kelvin connection to the
positive terminal of RSW.
Over Temperature Protection
The RT8482 has an Over Temperature Protection (OTP)
function to prevent excessive power dissipation from
overheating the device. The OTP function will shut down
switching operation when the die junction temperature
exceeds 150°C. The chip will automatically start to switch
again when the die junction temperature cools off.
Inductor Selection
The inductor used with the RT8482 should have a
saturation current rating appropriate to the maximum
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
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| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT8482.PDF ] | |
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