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Preliminary
RT9285A/B
Tiny Package, High Performance, Diode Embedded White LED Driver
General Description
The RT9285 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 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 N-MOSFET 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 and 8-Lead WDFN Package RoHS Compliant and 100% Lead (Pb)-Free
Applications
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Ordering Information
RT9285 Package Type QW : WDFN-8L 2x2 (W-Type) J6 : TSOT-23-6 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) Dimming A : Digital Pulse Dimming B : PWM Clock Dimming 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
AGND LX NC PGND
1 2 3
4 8
}RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
9
7 6
5
FB EN VOUT VDD
6 1 LX
5 2 GND
4 3 FB
}Suitable for use in SnPb or Pb-free soldering processes. }100%matte tin (Sn) plating.
WDFN-8L 2x2
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.
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.
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RT9285A/B
Typical Application Circuit
Preliminary
L1 10uH to 22uH
VIN 2.7V to 5.5V
RT9285A/B LX EN Chip Enable GND FB VDD VOUT
C1 1uF
C2 0.22uF to 1uF RSET 12.5
Functional Pin Description
Pin No. Pin Name WDFN-8L 1 2 -3, Exposed Pad (9) 4 5 TSOT-23-6 -1 2 --6 AGND LX GND NC PGND VDD Analog Ground Pin. LX Pin. Connect this Pin to an inductor. Minimize the track area to reduce EMI. Ground Pin. 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 8 3 FB ground as a current sense. Sense the current feedback voltage to set the current rating. -GND Exposed pad should be soldered to PCB board and connected to GND. Pin Function
6
5
VOUT
7
4
EN
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DS9285A/B-02 August 2007
Preliminary Function Block Diagram
Current Sense
RT9285A/B
1.0MHz OSC
Slope Compensation
OCP
OVP
PWM Logic
LX VOUT
VDD
UVLO/P GOOD
+ Timer Dimming Controller + Soft Start/Cla mping
EN FB
VREF
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 RT9285 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 (RT9285A) The digital pulse dimming is implemented by checking the low-level duration time of EN pin. As the duration time is in the range of TUP, the LED current will increase 1/16. If the duration time is in the range of TDOWN, the LED current will decrease 1/16. The high-level duration time of EN pin needs larger than TDELAY to make sure the logic can be detected correctly. As the LED current is set to MAX (16/ 16), it will keep MAX until the decreasing signal is detected. On the other hand, as the LED current is set to MIN (1/16), it will keep MIN until the increasing signal is detected. When the chip turns on, the initial state of LED current is MAX.
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RT9285A/B
Preliminary
Table 2 Feedback Voltage Increase Decrease Delay between steps Shutdown Time 0.5s to 75s 180s to 300s > 0.5s > 1ms Symbol TUP TDOWN TDELAY TSHDN
TDELAY EN TDOWM Shut-down IWLED 100% TUP 15/16 100% TSHDN Shut-down
Figure 1 PWM Dimming (RT9285B) For controlling the LED brightness, the RT9285B can perform the dimming control by applying a PWM signal to EN pin. A low pass filter is implemented inside chip to reduce the slew rate of ILED to prevent the audio noise. 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.
EN IWLED, AVG = Duty of EN IWLED
Figure 2 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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DS9285A/B-02 August 2007
Preliminary Absolute Maximum Ratings
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RT9285A/B
(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 -------------------------------------------------------------------------------------------------------------- 0.455W WDFN-8L 2x2 --------------------------------------------------------------------------------------------------------- 0.606W l Package Thermal Resistance (Note 4) TSOT23-6, JA -------------------------------------------------------------------------------------------------------- 220C/W WDFN-8L 2x2, JA --------------------------------------------------------------------------------------------------- 165C/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)
Operation Junction Temperature Range ------------------------------------------------------------------------- -40C to 125C Operation Ambient Temperature Range ------------------------------------------------------------------------- -40C to 85C
Electrical Characteristics
(VIN = 3.7V, FREQ left floating, TA = 25 C, 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 Cycle Reference Voltage Feedback Reference Voltage Diode Forward Voltage MOSFET On Resistance of MOSFET
Symbol V IN V UVLO IQ I IN I SHDN
Test Condition
Min 2.7 1.7
Typ -2 300 -2 -1 90 0.25 0.9 0.75
Max 5.5 2.3 450 2 5 3 --0.263 -1
Units V V A mA uA % MHz % V V
FB = 1.5V, No switch FB = 0V, Switch VEN < 0.4V V IN = 3V to 4.3V
-----85
f OSC
VREF VFW R DS(ON) IFW = 100mA
0.237 -0.5
To be continued
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RT9285A/B
Parameter Protection OVP Threshold OCP Control Interface EN Threshold Logic-Low Voltage VIL VOVP Symbol
Preliminary
Test Condition Min Typ Max Units
---
20 400
---
V mA
-1.4
---
0.4 --
V V
Logic-High Voltage VIH Digital Dimming (for RT9285A) Up Brightness Time Down Brightness Time Delay Between Steps Time Shut Down Delay Time TUP TDOWN TDELAY TSHDN Refer to Figure 1 Refer to Figure 1 Refer to Figure 1 Refer to Figure 1
0.5 180 0.5 1
-----
75 300 ---
s 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 T A = 25C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard.
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DS9285A/B-02 August 2007
Preliminary Typical Operating Characteristics
OVP vs. Input Voltage
20.8 20.4 20
RT9285A/B
Efficiency vs. Input Voltage
90 90%
4W-LED
85 85% 80 80%
Efficiency (%)
2.6 3 3.4 3.8 4.2 4.6 5 5.4 5.8 6.2
OVP (V)
75 75%
70% 70 65% 65 60% 60 55% 55 50% 50 2.5 3 3.5 4 4.5 5 5.5 6
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
25C 85C
0.98 0.96 0.94 0.92 0.90 0.88
2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6
2.6
3.1
3.6
4.1
4.6
5.1
5.6
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 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6
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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RT9285A/B
Preliminary
Feedback Reference Voltage vs. Input Voltage
253.5
Dimming Operation @ Decreace
VIN (2V/Div) VOUT (5V/Div)
VIN = 3.7V
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
EN (2V/Div) ILED (10mA/Div) Time (500s/Div)
Input Voltage (V)
Dimming Operation @ Increase
VIN (2V/Div) VOUT (5V/Div)
VIN = 3.7V
Inrush Current Response
VIN (2V/Div)
VIN = 3.7V
VOUT (5V/Div) EN (2V/Div) ILED (10mA/Div) Time (500s/Div) EN (2V/Div) IIN (100mA/Div) Time (500s/Div)
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DS9285A/B-02 August 2007
Preliminary Application Information
LED Current Control The RT9285A/B 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 VIN 2.7V to 5.5V
RT9285A/B
The inductor saturation current rating should be considered to cover the inductor peak current. Capacitor Selection Input and output ceramic capacitors of 1F are recommended for RT9285A/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. Output Voltage Control The output voltage of R9285 can be adjusted by the divider circuit on FB pin. Figure 6 shows a 2-level voltage control circuit for OLED application. The output voltage can be calculated by the following equations in Figure 6.
L1 10uH to 22uH VIN 2.7V to 5.5V
RT9285A/B LX EN Chip Enable GND FB VDD VOUT
C1 1uF
C2 0.22uF to 1uF RSET 12.5
RT9285A/B
C1 1uF
VOUT 15V
Figure 3. Application for Driving 4 Series WLEDs
VIN 2.7V to 5.5V
LX EN Chip Enable GND
VDD VOUT C2 0.22uF to 1uF FB R2 10k R1 590k
L1 10uH to 22uH
RT9285A/B LX EN Chip Enable GND FB VDD VOUT
C1 1uF
VOUT = 0.25 x R1 + R2 ; R2 > 10k R2 Figure 5. Application for Constant Output Voltage
C2 0.22uF to 1uF VIN RSET 12.5 GPIO RT9285A/B VDD VOUT RA R GPIO RB EN GND OLED
Figure 4. 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 RT9285A/B used for mobile phone. The inductor should have low core loss at 1MHz and low DCR for better efficiency.
DS9285A/B-02 August 2007
VEN
LX
FB
Figure 6. Application Circuit for Output Voltage Control and Related Equations
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RT9285A/B
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,
Preliminary
(1) } 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) } 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 RT9285. } The embedded antenna is far away and different side RT9285. } R1 should be placed as close as RT9285. } The through hole of RT9285's GND pin is recommended as large and many as possible.
(2)
VOUT = RA x {(0.25/RB) + (0.25-2.8)/RGPIO )} + 0.25 (3) 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 3. Suggested Resistance for Output Voltage Control RA RB RGPIO Conditions (k) (k) (k)
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 1100 18 495
L1 VIN C1 *1 LX GND GND RSET *4 FB 3 4 EN EN 1 2 6 5 *2 VDD VOUT C2 *3 WLEDs
Figure 7. TOP
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%. 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.
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Figure 8. Bottom
Preliminary Outline Dimension
RT9285A/B
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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RT9285A/B
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
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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DS9285A/B-02 August 2007

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