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Preliminary
RT9285C
Tiny Package, High Performance, Diode Embedded White LED Driver
General Description
The RT9285C is a high frequency asynchronous boost converter with internal diode, which can support 2 to 5 White LEDs for backlighting and OLED power supply. The Internal soft start function can reduce the inrush current. The device operates with 1MHz fixed switching frequency to allow small external components and to simplify possible EMI problems. The device comes with 20V over voltage protection to allow inexpensive and small-output capacitors with lower voltage rating. The LED current is initially set with the external sense resistor RSET , and the feedback voltage is 250 mV. Tiny package type TSOT-23-6, XDFN-8L 2x2 and WDFN-8L 2x2 packages provide the best solution for PCB space saving and total BOM cost.
Features
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VIN Operating Range : 2.7V to 5.5V Up to 85% Efficiency 22V Internal Power NMOS 1MHz Switching Frequency Built-in Diode Digital Dimming with Zero-Inrush Input UVLO Protection Output Over Voltage Protection Internal Soft Start and Compensation TSOT-23-6, 8-Lead XDFN and WDFN Package RoHS Compliant and 100% Lead (Pb)-Free
Applications
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Ordering Information
RT9285C Package Type QW : WDFN-8L 2x2 (W-Type) QX : XDFN-8L 2x2 (X-Type) J6 : TSOT-23-6 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) Note : Richtek Pb-free and Green products are :
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Cellular Phones Digital Cameras PDAs and Smart Phones Porbable Instruments MP3 Player OLED Power
Pin Configurations
(TOP VIEW)
VDD VOUT EN
GND
}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.
GND 1 LX 2 NC 3 PGND 4
8
7 6
5
9
FB EN VOUT VDD
6 1 LX
5 2 GND
4 3 FB
XDFN/WDFN-8L 2x2
TSOT-23-6
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.
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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RT9285C
Typical Application Circuit
Preliminary
L1 10uH to 22uH
VIN 2.7V to 5.5V
RT9285C LX EN Chip Enable GND PGND FB VDD VOUT
C1 1uF
C2 0.22uF to 1uF RSET 12.5
PGND pin for XDFN/WDFN-8L Packages
Function Pin Description
Pin No. Pin Name XDFN/WDFN-8L TSOT-23-6 1, Exposed Pad (9) 2 3 4 5 2 1 --6 GND LX NC PGND VDD Ground Pin. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. LX Pin. Connect this Pin to an inductor. Minimize the track area to reduce EMI. No Internal Connection. Power Ground Pin. Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input ripple. Output Voltage pin. The pin internally connects to OVP diode to limit output voltage while LEDs are disconnected. Chip Enable (Active High). Note that this pin has an internal pull-down resistance around 300k. Feedback Pin. Series connecting a resistor between WLED and ground as a current sense. Sense the current feedback voltage to set the current rating. Pin Function
6 7
5 4
VOUT EN
8
3
FB
0.5us < tHI
0.5us < tLO < 300us
EN
0
1
2
3
4
5
14
15
0
1 100% 15/16 Shutdown
Shutdown IWLED
100% 15/16 14/16 13/16 12/16
3/16
2/16
1/16
Figure 1. Operation of Digital Pulse Dimming Control
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Preliminary Function Block Diagram
Current Sense
RT9285C
1.0MHz OSC
Slope Compensation
OCP
OVP
PWM Logic
LX VOUT
VDD
UVLO/P GOOD
+ Timer Dimming Controller + Soft Start/ Clamping
EN FB
VREF
PGND
GND
Operation
Soft-Start The Soft-Start function is made by clamping the output voltage of error amplifier with another voltage source that is increased slowly from zero to near VIN in the Soft-Start period. Therefore, the duty cycle of the PWM will be increased from zero to maximum in this period. The softstart time is decided by a timer of 1.5ms. The charging time of the inductor will be limited as the smaller duty so that the inrush current can be reduced to an acceptable value. Over Voltage Protection The Over Voltage Protection is detected by a junction breakdown detecting circuit. Once VOUT goes over the detecting voltage, LX pin stops switching and the power NMOS is turned off. Then, the VOUT is clamped to be near VOVP. LED Current Setting The RT9285C regulates the LED current by setting the current sense resistor (RSET ) connecting to feedback and ground. The internal feedback reference voltage is 0.25V. The LED current can be set from following equation easily. ILED (mA) = 0.25/RSET
In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for RSET selection is shown below. Table 1. RSET Value Selection
ILED (mA) 5 10 12 15 20 RSET () 49.9 24.9 21 16.5 12.4
Digital Pulse Dimming Control RT9285C implements the pulse dimming method being used to control the brightness of white LEDs. There are 16 steps to set the current of white LEDs. The maximum LED current is up to 20mA that is sufficient for most application in backlight. The detail operation of brightness dimming is showed in the Figure 1. Current Limiting The current flow through the inductor as charging period is detected by a current sensing circuit. As the value over the current limiting, the NMOS will be turned-off so that the inductor will be forced to leave charging stage and enter discharging stage. Therefore, the inductor current will not increase over the current limiting.
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DS9285C-00 August 2007
RT9285C
Absolute Maximum Ratings
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Preliminary
(Note 1)
Supply Voltage, VIN ------------------------------------------------------------------------------------------------- -0.3 to 6V l LX Input Voltage ------------------------------------------------------------------------------------------------------ - 0.3V to 22V l Output Voltage ------------------------------------------------------------------------------------------------------- - 0.3V to 21V l The other pins -------------------------------------------------------------------------------------------------------- - 0.3V to 6V l Power Dissipation, PD @ TA = 25C TSOT23-6 -------------------------------------------------------------------------------------------------------------- 0.392W XDFN/WDFN-8L 2x2 ------------------------------------------------------------------------------------------------- 0.606W l Package Thermal Resistance (Note 4) TSOT23-6, JA -------------------------------------------------------------------------------------------------------- 255C/W XDFN/WDFN-8L 2x2, JA ------------------------------------------------------------------------------------------- 165C/W XDFN/WDFN-8L 2x2, JC ------------------------------------------------------------------------------------------- 20C/W l Junction Temperature ----------------------------------------------------------------------------------------------- 150C l Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------- 260C l Storage Temperature Range --------------------------------------------------------------------------------------- - 65C to 150C l ESD Susceptibility (Note 2) HBM (Human Body Mode) ----------------------------------------------------------------------------------------- 2kV MM (Machine Mode) ------------------------------------------------------------------------------------------------ 200V
Recommended Operating Conditions
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(Note 3)
Junction Temperature Range -------------------------------------------------------------------------------------- -40C to 125C Ambient Temperature Range -------------------------------------------------------------------------------------- -40C to 85C
Electrical Characteristics
(VIN = 3.7V, FREQ left floating, TA = 25C, Unless Otherwise specification)
Parameter System Supply Input Operation voltage Range Under Voltage Lock Out Quiescent Current Supply Current Shut Down Current Output Line Regulation Oscillator Operation Frequency Maximum Duty C ycle Reference Voltage Feedback Reference Voltage Diode Forward Voltage MOSFET On Resistance of MOSFET
Symbol VDD VUVLO IQ IIN ISHDN
Test Condition
Min 2.7 1.7
Typ -2 300 -2 -1 90 0.25
Max 5.5 2.3 450 2 5 3 --0.263
Units V V A mA uA % MHz % V
FB = 1.5V, No switch FB = 0V, Switch VEN < 0.4V VIN = 3V to 4.3V
-----85
fOSC
VREF VFW RDS(ON) IFW = 100mA
0.237
-0.5
0.9 0.75
-1
V
To be continued
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Preliminary
Parameter Protection OVP Threshold OCP Control Interface EN Threshold Logic-Low Voltage VIL Logic-High Voltage VIH EN Low Time for Dimming Delay Between Steps Time EN Low Time for Shut Down TLO THI TSHDN Refer to Figure 1 Refer to Figure 1 Refer to Figure 1 -1.4 0.5 0.5 1 -----VOV P --20 400 Symbol Test Condition Min Typ
RT9285C
Max Units
---
V mA
0.4 -300 ---
V V s s ms
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 TA = 25C on a low effective single layer thermal conductivity test board of JEDEC 51-3 thermal measurement standard. The case position of JC is on the package exposed pad.
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RT9285C
OVP vs. Input Voltage
20.8 20.4 20
Preliminary
Typical Operating Characteristics
Efficiency vs. Input Voltage
90
4W-LED
85 80
Efficiency (%)
2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5
OVP (V)
75 70 65 60 55 50 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5
19.6 19.2 18.8 18.4 18
Input Voltage (V)
Input Voltage (V)
Quiescent Current vs. Input Voltage
450 400 1.02 1.00
Frequency vs. Input Voltage
Quiescent Current (uA)
-40C
Frequency (MHz)
350 300 250 200 150 100 2.8 3.1 3.4 3.7 4 4.3
25C 85C
0.98 0.96 0.94 0.92 0.90 0.88
4.6
4.9
5.2
5.5
2.8
3.1
3.4
3.7
4
4.3
4.6
4.9
5.2
5.5
Input Voltage (V)
Input Voltage (V)
Enable Voltage vs. Input Voltage
0.84 0.83 0.82 17 16
Output Voltage vs. Output Current
Enable Voltage
Enable Voltage (V)
Output Voltage (V)
0.81 0.80 0.79 0.78 0.77 0.76 0.75 0.74 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5
15 14 13 12 11 10 5 15 25 35 45 55 65 75
Shutdown Voltage
Input Voltage (V)
Output Current (mA)
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Preliminary
RT9285C
Dimming Operation @ Decreace
Feedback Reference Voltage vs. Input Voltage
253.5
Feedback Reference Voltage (mV)
253.0 252.5 252.0 251.5 251.0 250.5 250.0 249.5 249.0 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5
VIN (2V/Div) VOUT (5V/Div)
VIN = 3.7V
EN (2V/Div) ILED (10mA/Div) Time (500s/Div)
Input Voltage (V)
Inrush Current Response
VIN (2V/Div)
VIN = 3.7V
VOUT (5V/Div) EN (2V/Div) IIN (100mA/Div) Time (500s/Div)
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RT9285C
Application Information
LED Current Control
Preliminary
Capacitor Selection Input and output ceramic capacitors of 1F are recommended for RT9285C 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. Output Voltage Control The output voltage of R9285C can be adjusted by the divider circuit on FB pin. Figure 5 shows a 2-level voltage control circuit for OLED application. The output voltage can be calculated by the following equations in Figure 5.
L1 10uH to 22uH
C2 0.22uF to 1uF FB R SET 12.5
The RT9285C regulates the LED current by setting the current sense resistor (RSET ) connecting to feedback and ground. The RT9284A/B feedback voltage (VFB) is 0.25V. The LED current (ILED) can be set by a resistor RSET . ILED = 0.25/RSET In order to have an accurate LED current, a precision resistor is preferred (1% is recommended).
L1 10uH to 22uH V IN 2.7V to 5.5V
RT9285C LX EN Chip Enable GND VDD VOUT
C1 1uF
V IN 2.7V to 5.5V
RT9285C LX EN VDD VOUT
C1 1uF
V OUT 15V
Figure 2. Application for Driving 4 Series WLEDs
V IN 2.7V to 5.5V
Chip Enable GND FB
C2 0.22uF to 1uF
R1 590k
R2 10k L1 10uH to 22uH
VOUT = 0.25 x R1 + R2 ; R2 > 10k R2 Figure 4. Application for Constant Output Voltage
V IN GPIO RT9285C VDD RSET 12.5 V EN VOUT RA R GPIO LX EN FB RB GND OLED
RT9285C LX EN Chip Enable GND FB VDD VOUT
C1 1uF
C2 0.22uF to 1uF
Figure 3. Application for Driving 5 Series WLEDs Inductor Selection The recommended value of inductor for 4 to 5WLEDs applications are 10H to 22H. For 3W LEDs, the recommended value of inductor is 4.7H to 22H. Small size and better efficiency are the major concerns for portable device, such as RT9285C used for mobile phone. The inductor should have low core loss at 1MHz and low DCR for better efficiency. The inductor saturation current rating should be considered to cover the inductor peak current.
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Figure 5. Application Circuit for Output Voltage Control and Related Equations
VOUT = RA x {(FB/RB) + (FB-GPIO)/RGPIO} + FB As GPIO = 0V, VOUT = RA x {(0.25/RB) + (0.25/RGPIO)} + 0.25 As GPIO = 2.8V,
(1)
(2)
VOUT = RA x {(0.25/RB) + (0.25-2.8)/RGPIO )} + 0.25 (3)
DS9285C-00 August 2007
Preliminary
As GPIO = 1.8V, VOUT = RA x {(0.25/RB) + (0.25-1.8)/ RGPIO)} + 0.25 (4) For Efficiency Consideration : Set RA = 990k, If 2 levels are 16V (GPIO = 0V) and 14V (GPIO = 1.8V) Get RB = 16k, RGPIO = 890k Table 2. Suggested Resistance for Output Voltage Control
Conditions Case A : Normal Voltage = 16V (GPIO = 0V) Dimming Voltage = 12V (GPIO = 1.8V) Case B : Normal Voltage = 16V (GPIO = 0V) Dimming Voltage = 12V (GPIO = 2.8V) 1200 19.5 840
Maximum Power Dissipation (W)
RT9285C
temperature of the die (125C) and TA is the maximum ambient temperature. The junction to ambient thermal resistance JA is layout dependent. For XDFN/WDFN 2x2 packages, the thermal resistance JA is 165 /W on the standard JEDEC 51-3 single layer thermal test board. The maximum power dissipation at TA = 25C can be calculated by following formula: PD(MAX) = (125C - 25C) / (165C/W) = 0.606 W for WDFN/ XDFN 2x2 packages PD(MAX) = (125C - 25C) / (255C/W) = 0.392 W for TSOT23-6 packages The maximum power dissipation depends on operating ambient temperature for fixed T J (MAX) and thermal resistance JA. For RT9285C packages, the Figure 6 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed.
0.8 0.7 0.6 0.5 0.4
RA (k)
RB (k)
RGPIO (k)
1100
18
495
XDFN/WDFN-8L 2x2 TSOT-23-6
Considering the output voltage deviation from the GPIO voltage tolerance, as GPIO voltage vibrated by 0 50mV and 1.8(2.8) 5% ,the output voltage could be kept within 2.5%. Thermal Considerations For continuous operation, do not exceed absolute maximum operation junction temperature. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula: PD(MAX) = ( TJ(MAX) - TA ) / JA Where T J(MAX) is the maximum operation junction temperature 125C, TA is the ambient temperature and the JA is the junction to ambient thermal resistance. For recommended operating conditions specification of RT9285C, where T J (MAX) is the maximum junction
0.3 0.2 0.1 0 0 25 50 75 100 125
Ambient Temperature (C)
Figure 6. Derating Curves for RT9285C Packages Layout guide } A full GND plane without gap break. } Traces in bold need to be routed first and should be kept as short as possible. } VDD to GND noise bypass : Short and wide connection for the 1uF MLCC capacitor between Pin 6 and Pin 2. } LX node copper area should be minimized for reducing EMI. (*1) } The input capacitor C1 should be placed as closed as possible to Pin 6. (*2)
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DS9285C-00 August 2007
RT9285C
Preliminary
} The output capacitor C2 should be connected directly from the Pin 5 to ground rather than across the LEDs. (*3) } FB node copper area should be minimized and keep far away from noise sources (Pin 1, Pin 5, Pin 6). (*4) } The Inductor is far away receiver and microphone. } The voice trace is far away RT9285C. } The embedded antenna is far away and different side RT9285C. } R1 should be placed as close as RT9285C. } The through hole of RT9285C's GND pin is recommended as large and many as possible.
L1 VIN C1 *1 LX GND RSET GND *4 FB 3 4 EN EN 1 2 6 5 *2 VDD VOUT C2 *3 WLEDs
Figure 7. TOP
Figure 8. Bottom
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DS9285C-00 August 2007
Preliminary Outline Dimension
RT9285C
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
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RT9285C
Preliminary
D
D2
L
E
E2 SEE DETAIL A
1
e A A1 A3
b
2
1
2
1
DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated.
Symbol A A1 A3 b D D2 E E2 e L
Dimensions In Millimeters Min 0.700 0.000 0.175 0.200 1.950 1.000 1.950 0.400 0.500 0.300 0.400 Max 0.800 0.050 0.250 0.300 2.050 1.250 2.050 0.650
Dimensions In Inches Min 0.028 0.000 0.007 0.008 0.077 0.039 0.077 0.016 0.020 0.012 0.016 Max 0.031 0.002 0.010 0.012 0.081 0.049 0.081 0.026
W-Type 8L DFN 2x2 Package
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DS9285C-00 August 2007
Preliminary
RT9285C
D
D2
L
E
E2 SEE DETAIL A
1
e A A1 A3
b
2
1
2
1
DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated.
Symbol A A1 A3 b D D2 E E2 e L
Dimensions In Millimeters Min 0.400 0.000 0.102 0.200 1.950 1.000 1.950 0.400 0.500 0.300 0.400 Max 0.500 0.050 0.152 0.300 2.050 1.250 2.050 0.650
Dimensions In Inches Min 0.016 0.000 0.004 0.008 0.077 0.039 0.077 0.016 0.020 0.012 0.016 Max 0.020 0.002 0.006 0.012 0.081 0.049 0.081 0.026
X-Type 8L DFN 2x2 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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