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PDF RT8470 Data sheet ( Hoja de datos )
| Número de pieza | RT8470 | |
| Descripción | High Brightness LED Driver | |
| Fabricantes | Richtek | |
| Logotipo |  |
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RT8470
1.2A/1A, Hysteretic, High Brightness LED Driver with
Internal Switch
General Description
The RT8470 is a high efficiency, continuous mode inductive
step-down converter, designed for driving single or multiple
series connected LEDs from a voltage source higher than
the LED voltage. It operates from an input voltage of 7V to
30V and employs hysteretic control with a high side current
sense resistor to set the constant output current.
The RT8470 includes an output switch and a high side
output current sensing circuit, which uses an external
resistor to set the nominal average output current. LED
brightness control is achieved with PWM dimming from
an analog or PWM input signal.
The RT8470 is available in a small TSOT-23-5 package or
a more thermal efficient SOP-8 (Exposed Pad) package.
Ordering Information
RT8470
Package Type
J5 : TSOT-23-5
SP : SOP-8 (Exposed Pad-Option 1)
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
RT8470GJ5
BS=DNN
BS= : Product Code
DNN : Date Code
RT8470GSP
RT8470
GSPYMDNN
RT8470GSP : Product Number
YMDNN : Date Code
Features
z 7V to 30V Input Voltage Range
z Hysteretic Control with High Side Current Sensing
z Internal N-MOSFETs with 350mΩ Low RDS(ON)
z 1A Output Current (For TSOT-23-5 Only)
z 1.2A Output Current (For SOP-8 (Exposed Pad) Only)
z Up to 97% Efficiency
z Typical ±5% LED Current Accuracy
z Analog or PWM Control Signal for LED Dimming
z 300Hz On-Board Ramp Generator
z Input Under Voltage Lockout
z Thermal Shutdown Protection
z RoHS Compliant and Halogen Free
Applications
z Automotive LED Lighting
z High Power LED Lighting
z Indicator and Emergency Lighting
z Architectural Lighting
z Low Voltage Industrial Lighting
z Signage and Decorative LED Lighting
Pin Configurations
(TOP VIEW)
VIN SENSE
54
23
LX GND ADJ
TSOT-23-5
VIN
SENSE
GND
ADJ
8
27
GND
36
9
45
GND
LX
NC
NC
SOP-8 (Exposed Pad)
DS8470-04 August 2011
www.richtek.com
1
1 page  
Typical Operating Characteristics
Efficiency vs. Input Voltage
10100%0 ILED = 1A, L = 33μH
7 LED
959%5
3 LED
909%0
858%5
1 LED
808%0
757%5
707%0
0
5 10 15 20 25 30 35
Input Voltage (V)
Efficiency vs. Input Voltage
10100%0 ILED = 500mA, L = 33μH
7 LED
959%5
3 LED
909%0
858%5
1 LED
808%0
757%5
707%0
0
5 10 15 20 25 30 35
Input Voltage (V)
Efficiency vs. Input Voltage
10100%0 ILED = 350mA, L = 33μH
7 LED
959%5
3 LED
909%0
1 LED
858%5
808%0
757%5
707%0
0
5 10 15 20 25 30 35
Input Voltage (V)
DS8470-04 August 2011
RT8470
Output Current Deviation vs. Input Voltage
5%5 ILED = 1A, L = 33μH
4%4
3%3
2%2
1%1 1 LED 3 LED
0%0
7 LED
-1-%1
-2-%2
-3-%3
-4-%4
-5-%5
0 5 10 15 20 25 30 35
Input Voltage (V)
Output Current Deviation vs. Input Voltage
5%5 ILED = 500mA, L = 33μH
4%4
3%3
2%2
1%1 1 LED 3 LED
0%0
-1%-1
7 LED
-2%-2
-3%-3
-4%-4
-5%-5
0
5 10 15 20 25 30 35
Input Voltage (V)
Output Current Deviation vs. Input Voltage
5%5 ILED = 350mA, L = 33μH
4%4
3%3
2%2 1 LED
1%1 3 LED
0%0
-1-%1 7 LED
-2-%2
-3-%3
-4-%4
-5-%5
0 5 10 15 20 25 30 35
Input Voltage (V)
www.richtek.com
5
5 Page 
RT8470
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJAis the junction to ambient
thermal resistance.
For recommended operating condition specifications of
the RT8470, the maximum junction temperature is 125°C
and TA is the ambient temperature. The junction to ambient
thermal resistance, θJA, is layout dependent. For TSOT-
23-5 packages, the thermal resistance, θJA, is 250°C/W
on a standard JEDEC 51-3 single-layer thermal test board
and 160°C/W on a standard JEDEC 51-7 four-layer thermal
test board. For SOP-8 (Exposed Pad) package, the
thermal resistance, θJA, is 75°C/W on a standard JEDEC
51-7 four-layer thermal test board. The maximum power
dissipation at TA = 25°C can be calculated by the following
formulas :
PD(MAX) = (125°C − 25°C) / (250°C/W) = 0.4W for
TSOT-23-5 package (single-layer PCB)
PD(MAX) = (125°C − 25°C) / (160°C/W) = 0.625W for
TSOT-23-5 package (four-layer PCB)
PD(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W for
SOP-8 (Exposed Pad) package
The maximum power dissipation depends on the operating
ambient temperature for fixed TJ(MAX) and thermal
resistance, θJA. For the RT8470 packages, the derating
curves in Figure 2 allow the designer to see the effect of
rising ambient temperature on the maximum power
dissipation.
1.5
1.4
1.3
1.2 SOP-8 (Exposed Pad)
1.1
1.0
0.9
0.8
0.7 TSOT23-5 (Four-Layer PCB)
0.6
0.5
0.4
0.3
0.2
0.1
TSOT23-5 (Single-Layer PCB)
0.0
0 25 50 75 100
Ambient Temperature (°C)
Figure 2. Derating Curve for Packages
125
Layout Considerations
For best performance of the RT8470, please abide the
following layout guide.
` The capacitor CIN, CADJ and external resistor, RS, must
be placed as close as possible to the VIN and SENSE
pins of the device respectively.
` The GND should be connected to a strong ground plane.
` Keep the main current traces as short and wide as
possible.
` The inductor (L) should be mounted as close to the
device with low resistance connections.
` The ADJ pin trace need to be kept far away from LX
terminal.
Place the resistor RS as close as
possible to VIN and SENSE pin.
Place the capacitor
CIN as close as
possible to VIN pin.
VIN
CIN
GND D
RS
VIN SENSE
LED+
54
123
LX GND ADJ
Place the capacitor
CADJ as close as
possible to ADJ pin.
CADJ
L
Figure 3. PCB Layout Guide
LED-
DS8470-04 August 2011
www.richtek.com
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet RT8470.PDF ] | |
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