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RT9293
Small Package, High Performance, Asynchronies Boost for 10 WLED Driver
General Description
The RT9293 is a high frequency, asynchronous boost converter. The internal MOSFET can support up to 10 White LEDs for backlighting and OLED power application, and the internal soft start function can reduce the inrush current. The device operates with 1-MHz fixed switching frequency to allow small external components and to simplify possible EMI problems. For the protection, the RT9293A provides 50V OVP and the RT9293B provides 50V/20V OVP to allow inexpensive and small-output capacitors with lower voltage ratings. The LED current is initially set with the external sense resistor RSET . The RT9293 is available in the tiny package type TSOT-23-6 and WDFN-8L 2x2 packages to provide the best solution for PCB space saving and total BOM cost.
Features
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VIN Operating Range : 2.5V to 5.5V Internal Power N-MOSFET Switch Wide Range for PWM Dimming (100Hz to200kHz) Minimize the External Component Counts Internal Soft Start Internal Compensation Under Voltage Protection Over Voltage Protection Over Temperature Protection Small TSOT-23-6 and 8-Lead WDFN Packages RoHS Compliant and Halogen Free
Applications
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Ordering Information
RT9293 () Package Type J6 : TSOT-23-6 QW : WDFN-8L 2x2 (W-Type)
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Cellular Phones Digital Cameras PDAs and Smart Phones and MP3 and OLED. Portable Instruments
Pin Configurations
(TOP VIEW)
VIN VOUT EN
6 5 4
Operating Temperature Range G : Green (Halogen Free with Commercial Standard) OVP Voltage Default : 50V (RT9293A/B) 20 : 20V (RT9293B) Feedback Voltage Reference A : 104mV B : 300mV
Note : Richtek Green products are :
}
2
3
LX GND FB
TSOT-23-6
GND 1 VIN 2 VOUT 3 EN 4
GND
8
9
7 6
5
LX NC FB GND
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. WDFN-8L 2x2 Suitable for use in SnPb or Pb-free soldering processes.
}
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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RT9293
Typical Application Circuit
L 22uH to 47uH D VOUT LX VIN CIN 2.2uF Chip Enable EN GND FB RSET VIN RT9293 VOUT
COUT 1uF 10 WLEDs
Functional Pin Description
Pin No. RT9293GJ6 1 2 3 4 5 6 -RT9293GQW 8 1, 5, 9 (Exposed pad) 6 4 3 2 7 Pin Name LX GND FB EN VOUT VIN NC Switching Pin. Ground Pin. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Feedback Pin, put a resistor to GND to setting the current. Chip Enable (Active High). Output Voltage Pin. Input Supply. No Internal Connection. Pin Function
Function Block Diagram
VIN LX
UVLO
OVP
VOUT
Internal Compensation Internal Soft Start
OCP OTP PWM Logic Control, Minimum On Time CurrentSense Driver GND Slope Compensation LPF Enable Logic Shutdown 20ms PWM Oscillator Reference Voltage
+ +
EA GM + VREF FB
1uA
Bias Current
EN
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RT9293
Absolute Maximum Ratings
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(Note 1)
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Supply Input Voltage, VIN ---------------------------------------------------------------------------------------------- -0.3V to 6V Switching Pin, LX -------------------------------------------------------------------------------------------------------- -0.3V to 50V VOUT ----------------------------------------------------------------------------------------------------------------------- -0.3V to 46V Other Pins ----------------------------------------------------------------------------------------------------------------- -0.3V to 6V Power Dissipation, PD @ TA = 25C TSOT-23-6 ----------------------------------------------------------------------------------------------------------------- 0.392W WDFN-8L 2x2 ------------------------------------------------------------------------------------------------------------ 0.606W Package Thermal Resistance (Note 3) TSOT-23-6, JA ----------------------------------------------------------------------------------------------------------- 255C/W WDFN-8L 2x2, JA ------------------------------------------------------------------------------------------------------- 165C/W WDFN-8L 2x2, JC ------------------------------------------------------------------------------------------------------ 20C/W Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------------ 260C Junction Temperature --------------------------------------------------------------------------------------------------- 150C Storage Temperature Range ------------------------------------------------------------------------------------------- -65C to 150C
Recommended Operating Conditions
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(Note 2)
Junction Temperature Range ------------------------------------------------------------------------------------------ -40C to 125C Ambient Temperature Range ------------------------------------------------------------------------------------------ -40C to 85C
Electrical Characteristics
(VIN = 3.7V, CIN = 2.2uF, COUT = 0.47uF, IOUT = 20mA, L = 22uH, TA = 25C, unless otherwise specified)
Parameter Input Voltage Under Voltage Lock Out UVLO Hystersis Quiescent Current Supply Current Shutdown Current Line Regulation Load Regulation Operation Frequency Maximum Duty Cycle Clock Rate Feedback Reference Voltage On Resistance RT9293A
Symbol VIN VUVLO
Conditions
Min 2.5 2 --
Typ -2.2 0.1 400 1 1 1 1 1 92 -104 300 0.7
Max 5.5 2.45 -600 2 4 --1.25 -200 114
Unit V V V uA mA uA % % MHz % kHz mV
IQ IIN ISHDN
FB = 1.5V, No Switching FB = 0V, Switching VEN < 0.4V VIN = 3 to 4.3V 1mA to 20mA
-----0.75 90 0.1 94
fOSC
VREF RT9293B RDS(ON) 285 -315 1.2
To be continued
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RT9293
Parameter EN Threshold EN Sink Current EN Hystersis Over-Voltage Threshold OVP = 50V RT9293B-20 VOVP IOCP TOTP TSHDN Logic-High Voltage Logic-Low Voltage Symbol VIH VIL IIH Conditions Min 1.4 ---42 16 1 ---Typ --1 0.1 46 17.5 1.2 160 30 20 Max -0.5 --50 20 ----Unit V V uA V V A C C ms
Over-Current Threshold OTP OTP Hystersis Shutdown Delay
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. The device is not guaranteed to function outside its operating conditions. Note 3. 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 point of JC is on the expose pad for the WDFN package.
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RT9293
Typical Operating Characteristics
Efficiency vs. Output Current
100 90 80
Efficiency vs. Input Voltage
100 90
VIN = 4.5V VIN = 4V
ILOAD = 30mA
80
Efficiency (%)
60 50 40 30 20 10 0 0 0.05 0.1 0.15 0.2 0.25 0.3
Efficiency (%)
70
70 60 50 40 30 20
ILOAD = 10mA ILOAD = 20mA
VOUT = 10V
10 0 2.5 3 3.5 4 4.5
VOUT = 34V
5 5.5
Output Current (A)
Input Voltage (V)
Output Voltage vs. Output Current
40 35
500 450 400 350 300 250
Quiescent Current vs. Input Voltage
30 25 20 15 VIN = 3.7V, VOUT = 34V 10 5 15 25 35 45 55 65 75 85
Quiescent Current (uA)
Output Voltage (V)
VFB = 1.5V
200 2.5 3 3.5 4 4.5 5 5.5
Output Current (mA)
Input Voltage (V)
Frequency vs. Input Voltage
1100 1050
Frequency vs. Temperature
1100 1050
Frequency (kHz)
Frequency (kHz)
1000 950 900 850
1000 950 900 850
ILED = 20mA
800 2.5 3 3.5 4 4.5 5 5.5
VIN = 3.7V, ILED = 20mA 800 -40 -25 -10 5 20 35 50 65 80 95 110 125
Input Voltage (V)
Temperature (C)
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RT9293
Reference Voltage vs. Input Voltage
0.32
Reference Voltage vs. Temperature
0.34 0.33
Reference Voltage (V)
Reference Voltage (V)
0.29
VOUT = 34V, IOUT = No Load
0.26
0.32 0.31 0.30 0.29 0.28 0.27
VIN = 3V VIN = 3.7V VIN = 4.2V
10WLED, ILED = 20mA
0.23
0.2
ILED = 20mA
0.17 2.5 3 3.5 4 4.5 5 5.5
0.26 -40 -15 10 35 60 85
Input Voltage (V)
Temperature (C)
Reference Voltage vs. Output Current
0.314 1.00
Enable Threshold vs. Input Voltage
0.98 0.96
VIN = 3V
Reference Voltage (V)
0.310
Rising
Enable Voltage (V)
0.94 0.92 0.90 0.88 0.86 0.84
0.306
VIN = 4.2V VIN = 3.7V
0.302 0.298 0.294
Falling
VOUT = 34V
0.290 0 5 10 15 20 25 30
0.82 0.80 2.5 3 3.5 4 4.5 5 5.5
Output Current (mA)
Input Voltage (V)
LED Current vs. Duty
25
Power On from EN
20
LED Current (mA)
15
VEN (2V/Div)
f f f f = 200Hz = 2kHz = 20kHz = 200kHz
10
5
VOUT (10V/Div)
6WLED, ILED = 20mA, VIN = 3.7V VIN = 3.7V, ILED = 20mA
0 10 20 30 40 50 60 70 80 90 100
0
Time (1ms/Div)
Duty (%)
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RT9293
Power Off from EN Ripple Voltage
VEN (2V/Div)
VIN (20mV/Div)
VOUT (10V/Div)
VIN = 3.7V, ILED = 20mA
VOUT (20mV/Div)
VIN = 3.7V, ILED = 20mA
Time (1ms/Div)
Time (500ns/Div)
PWM Dimming from EN
f = 200Hz
PWM Dimming from EN
f = 20kHz
VEN (4V/Div)
VEN (4V/Div)
ILED (10mA/Div)
VIN = 3.7V, ILED = 20mA
ILED (10mA/Div)
VIN = 3.7V, ILED = 20mA
Time (1ms/Div)
Time (10us/Div)
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RT9293
Applications Information
LED Current Setting The loop of Boost structure will keep the FB pin voltage equal to the reference voltage VREF. Therefore, when RSET connects FB pin and GND, the current flows from VOUT through LED and RSET to GND will be decided by the current on RSET , which is equal to following equation. ILED = VREF RSET filtered reference voltage is low and the offset can cause bigger variation of the output current. So the RT9293A is not recommend to be dimming by the EN pin. For the RT9293B, the minimum duty vs frequency is listed in 300mV following table.
EN
VA
+ EA -
To Controller
FB
Dimming Control a. Using a PWM Signal to EN Pin For the brightness dimming control of the RT9293, the IC provides typically 300mV feedback voltage when the EN pin is pulled constantly high. However, EN pin allows a PWM signal to reduce this regulation voltage by changing the PWM duty cycle to achieve LED brightness dimming control. The relationship between the duty cycle and FB voltage can be calculated as following equation. VFB = Duty x 300mV Where Duty = duty cycle of the PWM signal 300mV = internal reference voltage As shown in Figure 1, the duty cycle of the PWM signal is used to cut the internal 300mV reference voltage. An internal low pass filter is used to filter the pulse signal. And then the reference voltage can be made by connecting the output of the filter to the error amplifier for the FB pin voltage regulation. However, the internal low pass filter 3db frequency is 500Hz. When the dimming frequency is lower then 500Hz, VA is also a PWM signal and the LED current is controlled directly by this signal. When the frequency is higher than 500Hz, PWM is filtered by the internal low pass filter and the VA approach a DC signal. And the LED current is a DC current which elimate the audio noise. Two figures of PWM Dimming from EN are shown in Typical Operating Characteristics section and the PWM dimming frequency is 200Hz and 20kHz respectively. But there is an offset in error amplifier which will cause the VA variation. In low PWM duty signal situation, the
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Figure 1. Block Diagram of Programmable FB Voltage Using PWM Signal
Duty Minimum Dimming frequency < 500Hz Dimming frequency > 500Hz 4% 10%
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 2. As the DC voltage increases, the current f lows through R3 increasingly and the voltage drop on R3 increase, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2.8V and assume the RT9293 is selected which VREF is equal to 0.3V, the selection of resistors in Figure 2 sets the LED current from 21mA to 0mA. The LED current can be calculated by the following equation. VREF - ILED =
VIN 2.5V to 5.5V
R3 x (VDC - VREF ) R4 RSET
VOUT D COUT 1uF RT9293
L 10uH to 47uH
CIN 2.2uF VIN
LX VOUT EN WLEDs Chip Enable R3 10k R4 85k VDC Dimming 0V to 2.8V RSET 16
GND FB
Figure 2. Dimming Control Using a DC Voltage
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RT9293
c. Using a Filtered PWM signal
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 as Figure 3. 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. The LED current can be calculated by the following equation.
VREF - ILED =
VIN 2.5V to 5.5V
By the above equation and the application circuit shown in Figure 3, and assume the RT9293 is selected which VREF is equal to 0.3V. Figure 4 shows the relationship between the LED current and PWM duty cycle. For example, when the PWM duty is equal to 60%, the LED current will be equal to 8.6mA. When the PWM duty is equal to 40%, the LED current will be equal to 12.7mA. Constant Output Voltage Control The output voltage of the R9293 can be adjusted by the divider circuit on the FB pin. Figure 5 shows the application circuit for the constant output voltage. The output voltage can be calculated by the following Equations.
VOUT = VREF x R1 + R2 ; R2 >10k R2
L 10uH to 47uH VOUT D COUT 1uF RT9293 VIN LX VOUT EN Chip Enable
R3 x (VPWM x Duty - VREF ) R4 + RDC RSET
VOUT D COUT 1uF RT9293
L 10uH to 47uH
VIN 2.5V to 5.5V
CIN 2.2uF VIN
LX VOUT EN WLEDs
CIN 2.2uF
GND FB
GND Chip Enable FB R3 10k R4 3k RDC 82k 2.8V 0V PWM Signal CDC 1uF RSET 16
R1
R2
Figure 5. Constant Output Voltage Application
Figure 3. Dimming Control Using a Filtered PWM Signal
20 18 16
VIN
L 22uH
VOUT D COUT 1uF
CIN 2.2uF VIN
RT9293 LX VOUT FB 3 x 13 WLEDs RSET
LED Current (mA)
14 12 10 8 6 4 2 0 0 20 40 60 80 100
Chip Enable
GND EN
...
Figure 6. Application for Driving 3 X 13 WLEDs
PWM Duty (%)
Figure 4. PWM Duty Cycle vs. LED Current
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RT9293
Application for Driving 3 x 13 WLEDs The RT9293 can drive different WLEDs topology. For example, the Figure 6 shows the 3x13 WLEDs and total current is equal to 260mA. The total WLEDs current can be set by the RSET which is equal to following equation. ITotal = VREF RSET Inductor Selection The recommended value of inductor for 10 WLEDs applications is from 10uH to 47uH. Small size and better efficiency are the major concerns for portable devices, such as the RT9293 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. Capacitor Selection Input ceramic capacitor of 2.2uF and output ceramic capacitor of 1uF are recommended for the RT9293 applications for driving 10 series WLEDs. 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. 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, TA is the ambient temperature and the JA is the junction to ambient thermal resistance. For the recommended operating conditions specification of RT9293, the maximum junction temperature of the die is 125C. The junction to ambient thermal resistance JA is layout dependent. The junction to ambient thermal resistance for TSOT-23-6 package is 255C/W and for WDFN-8L 2x2 package is 165C/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) = 0.606W for WDFN-8L 2x2 packages PD(MAX) = (125C - 25C) / (255C/W) = 0.392W for TSOT-23-6 packages
Power Sequence In order to assure the normal soft start function for suppressing the inrush current the input voltage should be ready before EN pulls high. Soft-Start The function of soft-start is made for suppressing the inrush current to an acceptable value at the beginning of poweron. The RT9293 provides a built-in soft-start function by clamping the output voltage of error amplifier so that the duty cycle of the PWM will be increased gradually in the soft-start period. Current Limiting The current flow through inductor as charging period is detected by a current sensing circuit. As the value comes across the current limiting threshold, the N-MOSFET 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 threshold. OVP/UVLO/OTP 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 N-MOSFET will be turned off. Then, the VOUT will be clamped to be near VOVP. As the output voltage is higher than a specified value or input voltage is lower than a specified value, the chip will enter protection mode to prevent abnormal function. As the die temperature is higher then 160C, the chip also will enter protection mode. The power MOSFET will be turned off during protection mode to prevent abnormal operation.
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RT9293
The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance JA. For RT9293 packages, the Figure 7 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed.
0.8
The inductor should be placed as close as possible to the switch pin to minimize the noise coupling into other circuits. LX node copper area should be minimized for reducing EMI. GND
D L LX
The COUT should be connected directly from the output schottky diode to ground rather than across the WLEDs
COUT VIN CIN should be placed as closed as possible to VIN pin for good filtering.
1 2 3
6 5 4
VIN VOUT EN
Maximum Power Dissipation (W)
Single Layer PCB WDFN-8L 2x2
CIN
GND
0.7 0.6 0.5 0.4
RSET
FB
WLEDs
TSOT-23-6
0.3 0.2 0.1 0 0 25 50 75 100 125
FB node copper area should be minimized and keep far away from noise sources (LX pin) and RS should be as close as possible to FB pin.
Figure 8. The Layout Consideration of the RT9293
Ambient Temperature (C)
Figure 7. Derating Curves for RT9293 Packages
Layout Consideration For best performance of the RT9293, the following guidelines must be strictly followed. } Input and Output capacitors should be placed close to the IC and connected to ground plane to reduce noise coupling. } The GND and Exposed Pad should be connected to a strong ground plane for heat sinking and noise protection. } Keep the main current traces as possible as short and wide. } LX node of DC-DC converter is with high frequency voltage swing. It should be kept at a small area. } Place the feedback components as close as possible to the IC and keep away from the noisy devices.
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RT9293
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-23-6 Surface Mount Package
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RT9293
D2
D
L
E
E2 SEE DETAIL A
2 1 2 1
1
e A A1 A3
b
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
Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.
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