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RT9284A/B
Tiny Package, High Performance, Constant Current Switching Regulator for White LED
General Description
The RT9284A/B is a compact, high efficient and high integration LED driver. Internal 22V MOSFET can support 2 to 5 White LEDs for backlighting and camera flashing. Highly integration and internal compensation network minimizes as 5 external component counts. Optimized operation frequency can meet the requirement of small LC filters value and low operation current with high efficiency. Internal soft start function can reduce the inrush current. Tiny package type of TSOT-23-5 and TSOT-23-6 packages provide the best solution for PCB space saving and total BOM cost.
Features
VIN Operating Range : 2.7V to 5.5V Maximum Output Voltage up to 20V Dimming with Zero-inrush and Wide Frequency Range of 100 to 100kHz Over Voltage Protection Output Current up to 100mA at VOUT = 12V. Zero Shutdown Supply Current Minimize the External Component Small LC Filter Internal Soft Start RoHS Compliant and 100% Lead (Pb)-Free
Ordering Information
RT9284 () Package Type J5 : TSOT-23-5 J6 : TSOT-23-6 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) OVP Voltage 15 : 15V 20 : 20V FB Voltage A : 1.235V B : 0.25V
Note : Richtek Pb-free and Green products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. 100% matte tin (Sn) plating.
Applications
Camera Flash White LED Mobile Phone, Smart Phone LED Backlight PDA LED Backlight Digital Still Camera Camcorder
Pin Configurations
TOP VIEW
VDD 5 1 LX 2 GND EN 4 3 FB
TSOT-23-5
VDD OVP 6 1 LX 5 2 GND EN 4 3 FB
Marking Information
For marking information, contact our sales representative directly or through a Richtek distributor located in your area, otherwise visit our website for detail.
TSOT-23-6 Note : There is no pin1 indicator on top mark for TSOT-23-6 type, and pin 1 will be lower left pin when reading top mark from left to right.
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Typical Application Circuit
L1 4.7uH to 22uH VIN + 2.7V to 5.5V D1 SS0520 OVP 15V C2 1uF/16V ILED
C1 1uF 6
RT9284 1 LX VDD EN GND OVP 5
Dimming Control 100Hz-100kHz
4 2
FB 3 R1
Figure 1. Application for Driving 3 Series WLEDs
L1 4.7uH to 22uH VIN + 2.7V to 5.5V D1 SS0520 OVP 18V C2 1uF/25V ILED
C1 1uF 6
RT9284 1 LX VDD EN GND OVP 5 OVP 15V
R2 600k
Dimming Control 100Hz-100kHz
4 2
FB 3 R1
Figure 2. Application for Driving 4 Series WLEDs
L1 4.7uH to 22uH VIN + 2.7V to 5.5V D1 SS0520 OVP 20V C2 1uF/25V ILED
C1 1uF 6
RT9284B 1 LX VDD EN GND OVP 5
Dimming Control 100Hz-100kHz
4 2
FB 3 VFB = 0.25V R1
Figure 3. Application for Driving 5 Series WLEDs
L1 4.7uH to 22uH VIN + 2.7V to 5.5V D1 OVP SS0520 15V
VOUT 12V R1 130k C2 1uF/16V
C1 1uF 6 4 2
RT9284A 1 LX VDD EN GND OVP 5
FB 3
VFB = 1.235V R2 15k
Figure 4. Application for Constant Output Voltage
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Pin Description
Pin No. TSOT-23-5 TSOT-23-6 1 2 3 1 2 3 LX GND FB Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track area to reduce EMI. Ground Pin Feedback Reference Voltage Pin. Series connect a resistor between WLED and ground as a current sense. Sense the current feedback voltage to set the current rating. Chip Enable (Active High). Voltage sensing input to trigger the function of over voltage protection. Note that this pin is high impedance. There should be a pull low 100k resistor connected to GND when the control signal is floating. Over Voltage Protection Pin. Voltage sensing input to trigger the function of over voltage protection. Leave it unconnected to disable this function. Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input noise. Pin Name Pin Function
4
4
EN
-5
5 6
OVP VDD
Function Block Diagram
1.2MHz OSC VDD Current Bias BandGap Protection Circuit OVP OVP UVLO Timer 5ms + Buffer + EN Soft Start VREF FB GND ibias VREF
OCP 750mA
PWM Logic LX
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Absolute Maximum Ratings
(Note 1) -0.3V to 7V -0.3V to 22V -0.3V to 22V -0.3V to 6V 0.455W 0.455W 220C/W 220C/W 260C 150C -65C to 150C 2kV 200V Supply Input Voltage -----------------------------------------------------------------------------------------------------LX Input Voltage ----------------------------------------------------------------------------------------------------------OVP Voltage ---------------------------------------------------------------------------------------------------------------The Other Pins ------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25C TSOT-23-5 ------------------------------------------------------------------------------------------------------------------TSOT-23-6 ------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 4) TSOT-23-5, JA ------------------------------------------------------------------------------------------------------------TSOT-23-6, JA ------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 2) HBM (Human Body Mode) ---------------------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------------------
Recommended Operating Conditions
(Note 3)
Supply Input Voltage ------------------------------------------------------------------------------------------------------ 2.7V to 5.5V Junction Temperature Range -------------------------------------------------------------------------------------------- -40C to 125C Ambient Temperature Range -------------------------------------------------------------------------------------------- -40C to 85C
Electrical Characteristics
(VIN = 3.7V, TA = 25C unless otherwise specified)
Parameter System Supply Input Operation voltage Range Under Voltage Lock Out Quiescent Current Supply Current Shut Down Current Line Regulation Oscillator Operation Frequency Maximum Duty Cycle Dimming Frequency Reference Voltage
Symbol
Test Condition
Min
Typ
Max
Units
VDD VDD IDD IDD IDD FB = 1.5V, No switch FB = 0V, Switch VEN < 0.4V VIN : 3.0~4.3V
2.7 1.8 50 0.1 ---
-2.2 300 2 -3
5.5 2.5 1000 3 1 --
V V uA mA uA %
fOSC
0.9 85 100
1.2 ---
1.5 -100k
MHz % Hz
RT9284A Feedback Voltage (Note 5) RT9284B
1.173 0.237
1.235 0.25
1.296 0.263
V V
To be continued
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Parameter MOSFET On Resistance of MOSFET Protection OVP Threshold OVP Sink Current OCP Shut Down Voltage Enable Voltage VEN VEN for 2,3,4 WLEDs application VOVP for 5 WLED application 14 19 ---1.5 15 20 5 750 --16 21 --0.4 -V V A mA V V RDS(ON) -0.75 - Symbol Test Condition Min Typ Max Units
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. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. JA is measured in the natural convection at T A = 25C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Note 5. Floating the OVP pin to disable OVP function.
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Typical Operating Characteristics
Enable Voltage vs. Input Voltage
1.2 1.1
1.2
Shut Down Voltage vs. Input Voltage
1.1
-45C
Shut Down Voltage (V)
Enable Voltage (V)
-45C
1 0.9 0.8 0.7 0.6 0.5
1.0
25C
0.9
25C 85C
85C
0.8 0.7 0.6 0.5 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5
3
3.25 3.5 3.75
4
4.25 4.5 4.75
5
5.25 5.5
Input Voltage (V)
Input Voltage (V)
Efficiency vs. Input Voltage
84
22
LED Current vs. Input Voltage
4WLEDs, L = 10H
21.5
ILED = 20mA, L = 4.7H, DCR = 0.15
83.5 83
LED Current (mA)
3WLEDs
21 20.5 20 19.5 19 18.5 18
Efficiency (%)
82.5
4WLEDs
82 81.5 81 80.5 3 3.2 3.4 3.6 3.8 4 4.2 4.4
3
3.25 3.5 3.75
4
4.25 4.5 4.75
5
5.25 5.5
Input Voltage (V)
Input Voltage (V)
Maximum Duty Cycle vs. VDD
91% 91
2.7 2.5 2.3
POR (Rising/Falling) vs. Temperature
Maximum Duty Cycle (%)
90% 90 89% 89 88% 88
Rising
POR (V)
2.1 1.9 1.7 1.5
Falling
87 87% 86 86% 85 85%
3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5
-40 -30 -20 -10 0
10 20 30 40 50 60 70 80 90
VDD (V)
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Temperature (C)
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Switching Current vs. Input Voltage
2
Switching Frequency vs. Temperature
1.5
Switching Current (mA)
1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 3 3.25 3.5 3.75 4 4.25 4.5 4.75
25C
Switching Frequency (MHz)
1.8
-45C
1.45 1.4 1.35 1.3 1.25 1.2 1.15 1.1 1.05 1 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
85C
5
5.25 5.5
Input Voltage (V)
Temperature (C)
Feedback Voltage vs. Temperature
252.2 252
Dimming Operation
4WLEDs, VIN = 3.7V, ILED = 20mA, L = 10H
Feedback Voltage (mV)
251.8 251.6 251.4 251.2 251 250.8 250.6 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
EN
(5V/Div)
I IN
(50mA/Div)
I LED
(10mA/Div) f = 100Hz, Duty = 50%
Temperature (C)
Time (2ms/Div)
Dimming Operation
4WLEDs, VIN = 3.7V, ILED = 20mA, L = 10H
Dimming Operation
4WLEDs, VIN = 3.7V, ILED = 20mA, L = 10H
EN
EN
(5V/Div) (5V/Div)
I IN
(100mA/Div)
I IN
(100mA/Div)
(10mA/Div)
I LED
(10mA/Div)
I LED
f = 1kHz, Duty = 50% f = 10kHz, Duty = 50%
Time (400s/Div)
Time (40s/Div)
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Dimming Operation
4WLEDs, VIN = 3.7V, ILED = 20mA, L = 10H L = 10H (10V/Div) (5V/Div)
OCP
EN
VOUT I IN
(100mA/Div) (10mA/Div)
ILX
(500mA/Div)
I LED
f = 100kHz, Duty = 50%
LX
(20V/Div)
Time (4s/Div)
Time (25s/Div)
Inrush Current
4WLEDs, VIN = 3.0V, ILED = 20mA, L = 4.7H (2V/Div)
Inrush Current
4WLEDs, VIN = 4.3V, ILED = 20mA, L = 4.7H (2V/Div)
EN
EN
(2V/Div) (2V/Div) (5V/Div)
VIN
(5V/Div)
VIN VOUT I IN
(100mA/Div)
VOUT I IN
(100mA/Div)
Time (500s/Div)
Time (500s/Div)
Normal Operation
(5V/Div) (2V/Div) (2V/Div) 4WLEDs, VIN = 3.0V ILED = 20mA, L = 10H (5V/Div)
Normal Operation
4WLEDs, VIN = 3.7V ILED = 20mA, L = 10H
VOUT VIN LX
(10V/Div)
VOUT VIN LX
(10V/Div)
I IN
(100mA/Div)
I IN
(100mA/Div)
Time (400ns/Div)
Time (400ns/Div)
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Normal Operation
(5V/Div) (2V/Div) 4WLEDs, VIN = 4.3V ILED = 20mA, L = 10H (5V/Div) (2V/Div) 4WLEDs, VIN = 5.5V ILED = 20mA, L = 10H
Normal Operation
VOUT VIN LX
(10V/Div)
VOUT VIN LX
(10V/Div)
I IN
(100mA/Div)
I IN
(100mA/Div)
Time (400ns/Div)
Time (400ns/Div)
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Application Information
Power Sequence The RT9284A/B must take notice of the power sequence. The power sequence of RT9284A/B has to VDD early than EN or else the RT9284A/B maybe fall into the unknown state to result in RT9284A/B turn off.
V DD > 2.7V V DD EN > 1.5V EN EN < 0.4V
b. Using a DC Voltage Using a variable DC voltage to adjust the brightness is a popular method in some applications. The dimming control using a DC voltage circuit is shown in Figure 6. According to the Superposition Theorem, as the DC voltage increases, the voltage contributed to VFB increases and the voltage drop on R2 decreases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2.8V, the selection of resistors in Figure 6 sets dimming control of LED current from 20mA to 0mA.
V IN 2.7V to 5.5V C1 L1 4.7uH to 22uH D1 SS0520
V OUT
Figure 5 LED Current Control The RT9284A/B regulates the LED current by setting the current sense resistor (R1) connecting to feedback and ground. As shown in Table 1, the RT9284A feedback voltage (VFB) is 1.235V and the RT9284B feedback voltage (VFB) is 0.25V. The LED current (ILED) can be set by a resistor R1. In order to have an accurate LED current, a precision resistor is preferred (1% is recommended). Table 1
Version RT9284A RT9284B Feedback Reference Voltage VFB (V) 1.235 0.25 LED Current Setting ILED (A) ILED = 1.235/R1 ILED = 0.25/R1
V EN > 1.5V V EN < 0.4V RT9284A 6 4 2 VDD EN GND LX OVP 1 5
C2
ILED
FB 3 R3 13k V DC Dimming 0V to 2.8V
R2 10k R1 110
Figure 6. Dimming Control Using a DC Voltage for RT9284A The LED current can be calculated by the following equation. VFB - ILED = R2 x (VDC - VFB ) R3 R1
c. Using a Filtered PWM signal: Dimming Control a. Using a PWM Signal to EN Pin For controlling the LED brightness, the RT9284A/B can perform the dimming control by applying a PWM signal to EN pin. The internal soft start and the wide range dimming frequency from100 to100kHz can eliminate inrush current and audio noise when dimming. The average LED current is proportional to the PWM signal duty cycle. The magnitude of the PWM signal should be higher than the maximum enable voltage of EN pin, in order to let the dimming control perform correctly.
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Another common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming control. A filtered PWM signal acts as the DC voltage to regulate the output current. The recommended application circuit is shown in the Figure 7. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2.8V PWM signal should be above 2kHz. To fix the frequency of PWM signal and change the duty cycle of PWM signal can get different output current. Figure 8. shows the relationship between LED current and PWM duty cycle.
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RT9284A/B
V IN 2.7V to 5.5V C1 L1 4.7uH to 22uH D1 SS0520
Capacitor Selection
ILED
C2 RT9284A 6 1 VDD LX V EN > 1.5V V EN < 0.4V 4 2 EN GND OVP 5 R2 10k R3 10k R DC 3k 2.8V 0V PWM Signal C DC 1uF
Input and output ceramic capacitors of 1F are recommended for RT9284A/B applications. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wider voltage and temperature ranges. Diode Selection Schottky diode is a good choice for RT9284A/B because of its low forward voltage drop and fast reverse recovery. Using Schottky diode can get better efficiency. The highspeed rectification is also a good characteristic of Schottky diode for high switching frequency. Current rating of the diode must meet the root mean square of the peak current and output average current multiplication as following :
ID (RMS) (IOUT x IPEAK )
FB 3
R1 110
Figure 7. Filtered PWM Signal for LED Dimming Control of RT9284A The LED current can be calculated by the following equation.
VFB - ILED =
20 18 16
R2 x (VPWM x Duty - VFB ) R3 + RDC R1
The diode' s reverse breakdown voltage should be larger than the output voltage. SS0520 is recommended Schottky diode for rectifier. Layout Guide A full GND plane without gap break. VCC to GND noise bypass-Short and wide connection for the 1F MLCC capacitor between Pin6 and Pin2. Minimized LX node copper area to reduce EMI. Minimized FB node copper area and keep far away from noise sources.
LED Current (mA)
14 12 10 8 6 4 2 0 0 10 20 30 40 50 60 70 80 90 100
PWM Duty (%)
Figure 8 Inductor Selection The recommended value of inductor for 3 to 5 WLEDs applications are 4.7 to 22H. Small size and better efficiency are the major concerns for portable device, such as RT9284A/B used for mobile phone. The inductor should have low core loss at 1.2MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered.
Figure 9. Top Layer
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Figure 10. Bottom Layer
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Outline Dimension
H D L C B
b A A1 e
Symbol A A1 B b C D e H L
Dimensions In Millimeters Min 0.700 0.000 1.397 0.300 2.591 2.692 0.838 0.080 0.300 Max 1.000 0.100 1.803 0.559 3.000 3.099 1.041 0.254 0.610
Dimensions In Inches Min 0.028 0.000 0.055 0.012 0.102 0.106 0.033 0.003 0.012 Max 0.039 0.004 0.071 0.022 0.118 0.122 0.041 0.010 0.024
TSOT-23-5 Surface Mount Package
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H D L C B
b A A1 e
Symbol A A1 B b C D e H L
Dimensions In Millimeters Min 0.700 0.000 1.397 0.300 2.591 2.692 0.838 0.080 0.300 Max 1.000 0.100 1.803 0.559 3.000 3.099 1.041 0.254 0.610
Dimensions In Inches Min 0.028 0.000 0.055 0.012 0.102 0.106 0.033 0.003 0.012 Max 0.039 0.004 0.071 0.022 0.118 0.122 0.041 0.010 0.024
TSOT-23-6 Surface Mount Package
Richtek Technology Corporation
Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
Richtek Technology Corporation
Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com
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