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RT9302
60mA 3-Channel Pulse Dimming Current Source LED Driver
General Description
The RT9302 is a high performance constant current driver for white LED. It supports up to 3 white LEDs and regulates a constant current for uniform intensity. Each channel supports up to 20mA output current with 1% typical current accuracy and 0.7% typical current matching. The RT9302 provides a 16-step brightness dimming control. The LED current can be easily configured from 1.25mA to 20mA. The dimming of white LEDs' current can be achieved by applying a pulse signal to the EN pin. The LED current can be turned off by EN pin with pull low for 20s or longer. The typical leakage current is 4A while shutdown condition. RT9302 is available in a TSOT-23-8 package (1.0mm maximum height).
Features
Support Up to 3 White LEDs Output Current up to 20mA Each Channel Support Pulse and PWM Dimming 40mV Typical Current Source Dropout 1% Typical LED Current Accuracy 0.7% Typical LED Current Matching 16-Step Brightness Control Low Noise and EMI Low Shutdown Current 4A Typical RoHS Compliant and 100% Lead (Pb)-Free
Applications
Mobile Phone, DSC, MP3 White LED Backlighting LCD Display Supply
Ordering Information
RT9302 Package Type J8 : TSOT-23-8 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard)
Pin Configurations
(TOP VIEW)
LED2 LED1 NC EN
8 1
LED3
7 2
NC
6 3
GND
5 4
VIN
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. Note : There is no pin1 indicator on top mark for TSOT-23-8
TSOT-23-8
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.
type, and pin 1 will be lower left pin when reading top mark from left to right.
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RT9302
Typical Application Circuit
VIN 2.8 to 5.5V
4 CIN 4.7uF
VIN RT9302
6 3
LED1 EN GND LED2 LED3
7 8 1
Figure 1. For 3-WLEDs Application Circuit
VIN 2.8 to 5.5V
4 CIN 4.7uF
VIN RT9302 LED1 EN GND LED2 LED3 7 8 1
6 3
Figure 2. For 2-WLEDs Application Circuit
0.5us < tHI
0.5us < tLO < 10us
20us < tSHDN
EN
0 100%
1
2
3
4
5
14
15
0
1 100% 15/16 Shutdown
Shutdown ILEDx
15/16 14/16 13/16 12/16
3/16
2/16
1/16
Figure 3. Brightness control by pulse dimming. RT9302 implements 16 steps brightness control
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RT9302
Functional Pin Description
Pin Number Pin Name Pin Function 1 2, 5 3 4 6 7 8 LED3 NC GND VIN EN LED1 LED2 Current Sink for LED3. (If not in use, this pin must be connected to VIN) No Internal Connection. Power Ground. Input Voltage. Chip Enable. Current Sink for LED1. (If not in use, this pin must be connected to VIN) Current Sink for LED2. (If not in use, this pin must be connected to VIN)
Function Block Diagram
16 steps Pulse Dimming Controller 1MHz Oscillator
EN
Shut Down Delay
Low Dropout Current Source
UVLO GND
VIN
LED1 LED2 LED3
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RT9302
Absolute Maximum Ratings
(Note 1) -0.3V to 6V -0.3V to 6V 6V 0.455W 220C/W 260C 150C -65C to 150C 2kV 200V Supply Input Voltage -----------------------------------------------------------------------------------------------------Other I/O Pin Voltages --------------------------------------------------------------------------------------------------VIN, EN to GND -----------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25C TSOT-23-8 ------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 4) TSOT-23-8, 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)
Junction Temperature Range -------------------------------------------------------------------------------------------- -40C to 125C Ambient Temperature Range -------------------------------------------------------------------------------------------- -40C to 85C
Electrical Characteristics
(VIN = 3.6V, CIN = 1uF, ESR = 0.03, VF = 3.4V, ILED1 = ILED2 = ILED3 = 20mA, TA = 25C, unless otherwise specified)
Parameter Input Input Supply Voltage Under Voltage Lockout Threshold Under Voltage Lockout Hysteresis Shutdown Current Quiescent Current Output Output Current Current Matching Dropout Voltage Enable EN Threshold Voltage
Symbol
Test Condition
Min
Typ
Max
Units
VIN VIN falling
2.8 ---
-2.0 200 4 0.4
5.5 --10 --
V V mV A mA
ISHDN IQ
VEN = 0V VEN = High, IOUT = 0
---
ILED ILED-LED VLED
100% setting, VLED = 1V 100% setting, VLED = 1V 90% of full output current
18.4 -5 --
20 0 40
21.6 +5 150
mA % mV
Logic-High VIH Logic-Low VIL Logic-High THI Duration of EN Logic High for pulse dimming Duration of EN Logic Low for pulse dimming From EN Low to Shutdown VEN = 1.8V
1.5 -0.5 0.5 10 --
----16 1
-0.4 -10 20 --
V V s s s A
Time of EN Logic Logic-Low TLO Shutdown Delay EN Input Current TSHDN IEN
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RT9302
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.
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RT9302
Typical Operating Characteristics
Shutdown Current vs. Input Voltage
9 8
0.44
Quiescent Current vs. Input Voltage
0.43
-40C
Shutdown Current (uA)
7 6
Quiescent Current (mA)
25C
-40C 25C
0.42 0.41 0.4 0.39 0.38 0.37 0.36
85C
5 4 3 2 1 0 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2
85C
2.6 2.8
3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8
5 5.2
Input Voltage (V)
Input Voltage (V)
LED Current vs. Temperature
22 21.5 21
LED Current vs. Input Voltage
25 22.5 20
LED1 VF = 3.124V
LED2 VF = 3.224V
LED Current (mA)
LED Current (mA)
20.5 20 19.5 19 18.5 18 17.5 17 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
17.5 15 12.5 10 7.5 5 2.5 0 2.7 2.95 3.2 3.45 3.7 3.95 4.2 4.45 4.7 4.95 5.2
LED3 VF = 3.143V
Temperature (C)
Input Voltage (V)
Dimming Operation
Dimming Operation
EN (5V/Div)
EN (2V/Div)
I LED (5mA/Div)
I LED (5mA/Div)
VIN = 3.7V
VIN = 3.7V
Time (25s/Div)
Time (100s/Div)
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RT9302
Dimming Operation Turn-On
EN (2V/Div)
EN (2V/Div) I IN (50mA/Div)
I LED (5mA/Div)
I LED (10mA/Div)
VIN = 3.7V
VIN = 3.7V
Time (10s/Div)
Time (5s/Div)
Turn-Off
EN (2V/Div) I IN (50mA/Div)
I LED (10mA/Div)
VIN = 3.7V
Time (5s/Div)
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RT9302
Application Information
Input UVLO The input operating voltage range of the RT9302 is 2.8V to 5.5V. An input capacitor at the VIN pin could reduce ripple voltage. It is recommended to use a ceramic 1F or larger capacitance as the input capacitor. This IC provides an under voltage lockout (UVLO) function to prevent it from unstable issue when startup. The UVLO threshold of input falling voltage is set at 2V typically with a hysteresis 0.2V. Output Current RT9302 provides a constant output current for white LED. Figure 1 shows a typical application circuit for 3 white LEDs. Each channel supports up to 20mA output current and regulates a constant current for uniform intensity. For two or one LED application, the non-used channel must be connected to VIN as shown in Figure 2. Brightness Dimming Control The RT9302 provides a 16-step brightness dimming control. The LED current can be easily configured from 1.25mA to 20mA. The dimming of white LEDs' current can be achieved by applying a pulse signal to the EN pin. Figure 3 shows the configuration of the 16-step pulse dimming control operation. The output current is set at 100% of 20mA typical output current when EN pin pull high initially from shutdown condition. The step change of pulse dimming can be implemented by EN pin changing with a logic Low pulse. Each step change 1/16 of full output current setting. The output current change of pulse dimming is designed in decreasing sequence in terms of (16/16, 15/16, ....., 1/16) and then (16/16, 15/16, .....) cycle by cycle. The duration of logic Low pulse is between 0.5us and 10s. The duration of EN logic High pulse should be longer than 0.5s. The LED current can be turned off by EN pin with pulling low for 20s or longer. The typical leakage current is 4A while shutdown condition. Layout Consideration For best performance, careful PCB layout is necessary. All peripheral components should be placed as close to the IC as possible. A short connection is highly recommended. The following guidelines should be strictly followed when designing a PCB layout for the RT9302. 1. All the traces of LED and VIN running from chip to LEDs should be wide and short to reduce the parasitic connection resistance. 2. Input capacitor (CIN) should be placed close to VIN and connected to ground plane. The anodes of LEDs must be connected to CIN, not battery directly. 3. The GND should be connected to a strong ground plane for heat sinking and noise protection.
All the traces of LED and VIN running from chip to LEDs should be wide and short to reduce the parasitic connection resistance. Input capacitor (CIN) should be placed close to VIN and connected to ground plane. The Anodes of LEDs must connect to CIN, not battery directly.
LED3 NC GND
1 2 3 4
8 7 6 5
LED2 LED1 EN NC GPIO
Battery CIN
VIN
Ground Plane The GND should be connected to a strong ground plane for heat sinking and noise protection.
Figure 4. PCB Layout Guide
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RT9302
Outline Dimension
H D L C B
b A e A1
Symbol A A1 B b C D e H L
Dimensions In Millimeters Min 0.700 0.000 1.397 0.220 2.591 2.692 0.585 0.080 0.300 Max 1.000 0.100 1.803 0.380 3.000 3.099 0.715 0.254 0.610
Dimensions In Inches Min 0.028 0.000 0.055 0.009 0.102 0.106 0.023 0.003 0.012 Max 0.039 0.004 0.071 0.015 0.118 0.122 0.028 0.010 0.024
TSOT-23-8 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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