RT8470 Datasheet PDF - Richtek

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RT8470
Richtek

Part Number RT8470
Description High Brightness LED Driver
Page 13 Pages


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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
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RT8470
Typical Application Circuit
VIN
7V to 30V
CIN
RT8470
VIN SENSE
ADJ
GND
LX
RS
optional
D
L
Functional Pin Description
Pin No.
SOP-8
(Exposed Pad)
TSOT-23-5
71
Pin Name
LX
Pin Function
Switch Output Terminal. Drain of internal N-MOSFETs.
3, 8,
9 (Exposed Pad)
2
GND
Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
Dimming Control Input :
4
3 ADJ
--- Analog signal input for analog control of PWM dimming.
--- PWM signal input for digital PWM dimming.
2 4 SENSE Output Current Sense Terminal. Sense LED string current.
1
5 VIN
Supply Input Voltage.
5, 6
-- NC
No Internal Connection.
Function Block Diagram
VIN
Regulator
Bandgap
UVLO
UVLO
VCC
1.25V
+
-
Ramp Gen.
+ Dimming
ADJ -
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2
UVLO
Dimming
SENSE
LX
GND
DS8470-04 August 2011



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RT8470
Absolute Maximum Ratings (Note 1)
z Supply Input Voltage, VIN ------------------------------------------------------------------------------------- 0.3V to 33V
z Switch Voltage, LX --------------------------------------------------------------------------------------------- 0.3V to (VIN + 0.7V)
z Sense Voltage, SENSE -------------------------------------------------------------------------------------- (VIN 5V) to (VIN + 0.3V)
z All Other Pins ----------------------------------------------------------------------------------------------------- 0.3V to 6V
z Power Dissipation, PD @ TA = 25°C
SOP-8 (Exposed pad) ----------------------------------------------------------------------------------------- 1.333W
TSOT-23-5 (Single-layer PCB) ------------------------------------------------------------------------------- 0.400W
TSOT-23-5 (Four-layer PCB) --------------------------------------------------------------------------------- 0.625W
z Package Thermal Resistance (Note 2)
SOP-8 (Exposed pad), θJA ----------------------------------------------------------------------------------- 75°C/W
SOP-8 (Exposed pad), θJC ----------------------------------------------------------------------------------- 15°C/W
TSOT-23-5, θJA (Single-layer PCB) ------------------------------------------------------------------------- 250°C/W
TSOT-23-5, θJC (Single-layer PCB) ------------------------------------------------------------------------- 130°C/W
TSOT-23-5, θJA (Four-layer PCB) --------------------------------------------------------------------------- 160°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
Recommended Operating Conditions (Note 4)
z Supply Input Voltage, VIN ------------------------------------------------------------------------------------- 7V to 30V
z Junction Temperature Range --------------------------------------------------------------------------------- 40°C to 125°C
Electrical Characteristics
(VIN = 12V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min Typ Max Unit
Mean Current Sense Threshold
Voltage
Sense Threshold Hysteresis
VSENSE
Measure on SENSE Pin with
Respect to VIN. VADJ is Floating.
VSENSEHYS
95
--
100 105 mV
±15 --
%
Low-Side Switch On-Resistance RDS(ON)
-- 350 -- mΩ
Low-Side Switch Leakage Current
Under Voltage Lockout Threshold
Rising
Under Voltage Lockout Threshold
Hysteresis
VUVLO
ΔVUVLO
VLX = 5V
-- 0.01 10 μA
-- 5.2 --
V
-- 400 -- mV
Ramp Frequency
fRAMP
-- 300 --
Hz
ADJ Input Threshold Logic-High VADJ, H
Voltage
Logic-Low VADJ, L
1.4
--
--
--
--
0.2
V
Analog Dimming Range
0.3 -- 1.3 V
Analog Dimming
Threshold Voltage
Logic-High
Logic-Low
-- 1.2 1.3
0.3 0.4 --
V
DS8470-04 August 2011
To be continued
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RT8470
Parameter
Minimum Switch On Time
Minimum Switch Off Time
Quiescent Input Current with
Output Off
Quiescent Input Current with
Output Switching
Internal Propagation Delay
Sense Pin Input Current
Thermal Shutdown
Thermal Shutdown Hysteresis
Symbol
tON(MIN)
tOFF(MIN)
IVIN, Off
IVIN, On
tPD
ISENSE
TSD
ΔTSD
Test Conditions
LX Switch On
LX Switch Off
Min
--
--
VADJ = 0V
ADJ Pin Floating, fSW = 250kHz,
VIN = 8V
VSENSE = VIN – 0.1V
--
--
--
--
--
--
Typ
210
170
450
1000
25
300
150
30
Max
--
--
--
--
--
--
--
--
Unit
ns
ns
μA
μA
ns
nA
°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 natural convection at TA = 25°C on a single-layer and four-layer test board of JEDEC 51 thermal
measurement standard. The measurement case position of θJC is on the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
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DS8470-04 August 2011



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