RT9292 Small Package, High Performance, Asyn-Boost Converter for 6 White LEDs General Description Features The RT9292 is a high frequency and high efficiency asynchronous boost converter for WLED driving application. It integrates a 28V MOSFET to support up to 6 White LEDs for panel backlighting and OLED power applications. Besides, an internal soft start function is integrated to reduce the inrush current. Moreover, the device operates with 1MHz fixed switching frequency for the use of small external components and better EMI performance. For lower voltage application, the IC provides a 26V over voltage protection function for using the lowcost and small output capacitors. The LED current is initially set by the external sense resistor (RSET), and the z feedback voltage for the RT9292 series will be 104mV and 330mV respectively. The RT9292 is available in TSOT23-6 and WDFN-8L 2x2 tiny packages to achieve best solution for PCB space and total BOM cost saving considerations. z z z z z z z z z z z VIN Operating Range : 2.5V to 5.5V 28V Internal Power N-MOSFET Switch Wide Range PWM Dimming (200Hz to 200kHz) Minimize the External Component Counts Internal Soft Start Internal Compensation Under Voltage Protection Over Voltage Protection Over Temperature Protection Internal Schottky Diode Small TSOT-23-6 and 8-Lead WDFN Packages RoHS Compliant and Halogen Free Applications z z z z Cellular Phones Digital Cameras PDAs and Smart Phones and MP3 and OLED. Portable Instruments Ordering Information Pin Configurations RT9292 Package Type J6 : TSOT-23-6 QW : WDFN-8L 2x2 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Feedback Reference Voltage B : 104mV D : 330mV Note : (TOP VIEW) VIN VOUT EN 6 5 4 2 3 LX GND FB TSOT-23-6 RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. GND 1 VIN 2 VOUT 3 EN 4 GND Richtek products are : 9 8 7 6 5 LX NC FB GND WDFN-8L 2x2 Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. DS9292-02 April 2011 www.richtek.com 1 RT9292 Typical Application Circuit L 22uH Optional LX VOUT COUT 0.22uF VIN CIN 2.2uF RT9292 6 WLEDs Chip Enable EN GND FB RSET Functional Pin Description Pin No. Pin Name RT9292 GJ6 RT9292 GQW 1 8 2 1, 5, 9 (Exposed pad) 3 Pin Function LX Switching Pin. GND Ground Pin. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 6 FB Feed Back Pin, put a resistor to GND to set the current. 4 4 EN Chip Enable (Active High). 5 3 VOUT Output Voltage Pin. 6 2 VIN Input Supply. -- 7 NC No Internal Connection, keep floating. Function Block Diagram LX VIN UVLO OVP VOUT V F = 0.7V OCP OTP Logic Control, Minimum On Time PWM CurrentSense + + EA GM Driver GND + - Slope Compensation LPF Enable Logic 10ms Shutdown V REF 1uA FB www.richtek.com 2 EN DS9292-02 April 2011 RT9292 Absolute Maximum Ratings z z z z z z z z z (Note 1) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------ -0.3V to 6V LX, VOUT Pins ------------------------------------------------------------------------------------------------------------- -0.3V to 28V Other Pins ------------------------------------------------------------------------------------------------------------------- -0.3V to 6V Power Dissipation, PD @ TA = 25C TSOT-23-6 ------------------------------------------------------------------------------------------------------------------WDFN-8L 2x2 -------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) TSOT-23-6, JA ------------------------------------------------------------------------------------------------------------WDFN-8L 2x2, JA -------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) ---------------------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------------------ Recommended Operating Conditions z z 0.392W 0.606W 255C/W 165C/W 260C 150C -65C to 150C 2kV 200V (Note 4) Junction Temperature Range -------------------------------------------------------------------------------------------- -40C to 125C Ambient Temperature Range -------------------------------------------------------------------------------------------- -40C to 85C Electrical Characteristics (VIN = 3.7V, CIN = 2.2uF, COUT = 0.22uF, IOUT = 20mA, L = 22uH, TA = 25C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Input Voltage V IN 2.5 -- 5.5 V Under Voltage Lock Out V UVLO 2.0 2.2 2.4 V -- 0.1 -- V 400 600 uA 2 mA UVLO Hysteresis Quiescent Current IQ FB = 1.5V, No Switching -- Supply Current IIN FB = 0V, Switching -- Shutdown Current ISHDN VEN < 0.4V -- 1 4 uA Line Regulation VIN = 3.0 to 4.3V -- 1 -- % Load Regulation 1mA to 20mA -- 1 -- % 0.75 1.0 1.25 MHz 90 92 -- % 94 104 114 313 330 347 -- 0.5 1.0 Operation Frequency fOSC Maximum Duty Cycle Feedback RT9292B V REF Reference Voltage RT9292D On Resistance RDS(ON) mV EN Logic-High Voltage V IH 1.4 -- -- Threshold Logic-Low Voltage V IL -- -- 0.5 V To be continued DS9292-02 April 2011 www.richtek.com 3 RT9292 Parameter Symbol Test Conditions Min Typ Max Unit EN Sink Current IIH -- 1 -- uA EN Low Time to Shutdown T SHDN -- 10 -- ms 0.2 -- 200 kHz 25 26 28 V -- 1 -- V Dimming Frequency Over-Voltage Threshold V OVP Over-Voltage Hysteresis Over-Current Threshold IOCP 500 700 -- mA OTP T OTP -- 160 -- C -- 30 -- C -- 0.7 -- V OTP Hysteresis Schottky Forward Voltage VF IDiode = 100mA 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. 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. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. www.richtek.com 4 DS9292-02 April 2011 RT9292 Typical Operating Characteristics Efficiency vs. Output Current Efficiency vs. Input Voltage 90 90 85 VIN = 3.7V 75 VIN = 3V 70 65 80 Efficiency (%) 80 Efficiency (%) Load = 30mA VIN = 4.2V 85 60 Load = 20mA 75 Load = 10mA 70 65 60 55 55 VOUT = 20V, L = 22uH VOUT = 20V, L = 22uH 50 50 00 5 0.005 10 0.01 15 0.015 20 0.02 25 0.025 30 0.03 2.5 3 3.5 OutputCurrent Current(mA) (A) Output 4 4.5 5 5.5 Input Voltage (V) Efficiency vs. Output Current Efficiency vs. Input Voltage 90 90 VIN = 4.2V 85 85 Load = 10mA 80 VIN = 3.7V 75 70 VIN = 3V 65 Efficiency (%) Efficiency (%) 80 60 75 70 Load = 20mA 65 60 55 Load = 30mA 50 55 45 VOUT = 20V, L = 33uH VOUT = 20V, L = 33uH 40 50 0 0.005 0.01 0.015 0.02 0.025 2.5 0.03 3 3.5 4 4.5 5 5.5 Input Voltage (V) Output Current (A) Output Voltage vs. Output Current Quiescent Current vs. Input Voltage 22 700 650 Quiescent Current (uA) Output Voltage (V) 20 18 16 14 12 600 550 500 450 400 350 300 250 VIN = 3.7V 10 200 5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 Output Current (mA) DS9292-02 April 2011 2.6 3.1 3.6 4.1 4.6 5.1 Input Voltage (V) www.richtek.com 5 RT9292 Switching Frequency vs. Input Voltage Switching Frequency vs. Temperature 1100 990 Switching Frequency (kHz) Switching Frequency (kHz) 1000 980 970 960 950 940 1050 1000 950 900 850 6WLED, ILED = 20mA 6WLED, ILED = 20mA, VIN = 3.7V 930 800 2.5 3 3.5 4 4.5 5 5.5 -40 -20 0 Input Voltage (V) 20 40 60 80 100 120 Temperature (C) Reference Voltage vs. Input Voltage Reference Voltage vs. Temperature 0.340 0.340 0.338 0.336 Reference Voltage (V) Reference Voltage (V) VIN = 3V 0.336 0.334 0.332 VIN = 3.7V 0.332 VIN = 4.2V 0.328 0.324 6WLED, ILED = 20mA 6WLED, ILED = 20mA 0.330 0.320 2.5 3 3.5 4 4.5 5 5.5 -40 -20 Input Voltage (V) 20 40 60 80 100 120 Temperature (C) Enable Threshold Voltage vs. Input Voltage Reference Voltage vs. Output Current 0.340 1.00 VIN = 3.7V 0.338 0.336 VIN = 3V VIN = 4.2V 0.334 0.332 Enable Threshold Voltage (V) Reference Voltage (V) 0 0.98 Rising 0.96 0.94 0.92 0.90 Falling 0.88 VOUT = 20V 0.330 0.86 0 5 10 15 20 Output Current (mA) www.richtek.com 6 25 30 2.6 3.1 3.6 4.1 4.6 5.1 Input Voltage (V) DS9292-02 April 2011 RT9292 LED Current vs. Duty OVP Voltage vs. Input Voltage 25 27.0 20 LED Current (mA) OVP Voltage (V) 26.5 26.0 25.5 25.0 15 f f f f 10 = 200Hz = 2kHz = 20kHz = 200kHz 5 24.5 6WLED, ILED = 20mA, VIN = 3.7V 24.0 0 2.5 3 3.5 4 4.5 5 5.5 0 10 20 30 40 50 60 70 Input Voltage (V) Duty (%) Power On from EN Power Off from EN 80 90 100 6WLED, ILED = 20mA, VIN = 3.7V VEN (2V/Div) VEN (2V/Div) VOUT (20V/Div) VOUT (10V/Div) I IN (100mA/Div) ILX (200mA/Div) 6WLED, ILED = 20mA, VIN = 3.7V Time (500us/Div) Time (1ms/Div) Ripple Voltage Ripple Voltage VIN (20mV/Div) VIN (20mV/Div) VOUT (100mV/Div) VOUT (100mV/Div) COUT = 1uF, ILED = 20mA, VIN = 3.7V Time (500ns/Div) DS9292-02 April 2011 COUT = 0.22uF, ILED = 20mA, VIN = 3.7V Time (500ns/Div) www.richtek.com 7 RT9292 PWM Dimming from EN PWM Dimming from EN f= 20kHz, ILED = 20mA, VIN = 3.7V f= 200Hz, ILED = 20mA, VIN = 3.7V VEN (2V/Div) VEN (2V/Div) I LED (10mA/Div) I LED (10mA/Div) Time (1ms/Div) www.richtek.com 8 Time (10us/Div) DS9292-02 April 2011 RT9292 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 : V ILED = REF RSET filtered reference voltage is low and the offset can cause bigger variation of the output current. So RT9292B is not recommend to be dimming by EN pin. For RT9292D the minimum duty vs frequency is list in following table. 330mV EN VA Dimming Control a. Using a PWM Signal to EN Pin For the brightness dimming control of the RT9292, the IC provides typically 330mV 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 330mV Where Duty = duty cycle of the PWM signal 330mV = internal reference voltage As shown in Figure 1, the duty cycle of the PWM signal is used to cut the internal 330mV 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 DS9292-02 April 2011 + EA - To Controller FB Figure 1. Block Diagram of Programmable FB Voltage Using PWM Signal Duty Minimum Dimming frequency < 500Hz Dimming frequency > 500Hz 4% 12% 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 pass 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 RT9292 is selected which VREF is equal to 0.33V, the selection of resistors in Figure 2 sets the LED current from 20.55mA to 0mA. The LED current can be calculated by the following Equation : R3 x (VDC - VREF ) VREF - R4 ILED = RSET V IN 2.5V to 5.5V C IN 2.2uF V OUT L C OUT 1uF RT9292 LX VIN GND VOUT WLEDs EN FB Chip Enable R3 10k R4 75k R SET 18.2 V DC Dimming 0V to 2.8V Figure 2. Dimming Control Using a DC Voltage for the RT9292 www.richtek.com 9 RT9292 c. Using a Filtered PWM signal 20 Another common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming control. 18 ILED R3 x (VPWM x Duty - VREF ) VREF - R4 + RDC = RSET V IN 2.5V to 5.5V C IN 2.2uF V OUT EN FB WLEDs R3 10k R DC 68k 10 8 6 4 2 0 0 R SET 18.2 40 60 80 100 PWM Duty (%) Constant Output Voltage Control V IN 2.5V to 5.5V V OUT L C DC 1uF 2.8V 0V PWM Signal C IN 2.2uF By the above equation and the application circuit shown in Figure 3, and assume the RT9292D is selected which VREF is equal to 0.33V. 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 8.2mA. When the PWM duty is equal to 40%, the LED current will be equal to 12.3mA. C OUT 1uF RT9292 LX VIN R1 GND VOUT Figure 3. Filtered PWM Signal for LED Dimming Control of the RT9292 www.richtek.com 10 20 VOUT = VREF x R1 + R2 ; R2 > 10k R2 Chip Enable R4 6.8k 12 The output voltage of RT9292 can be adjusted by the divider circuit on FB pin. Figure 5 shows the application circuit for the constant output voltage. The output voltage can be calculated by the following Equations : C OUT 1uF GND VOUT 14 Figure 4. LED Current Variation with the PWM Dimming on FB L RT9292 LX VIN LED Current (mA) 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 : 16 EN FB Chip Enable R2 Figure 5. Application for Constant Output Voltage Soft-Start The function of soft-start is made for suppressing the inrush current to an acceptable value at the beginning of poweron. The soft-start function is built-in the RT9292 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. DS9292-02 April 2011 RT9292 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 > 160C, the chip also will enter protection mode. The power MOSFET will be turned off during protection mode to prevent abnormal operation. Inductor Selection The recommended value of inductor for 6 WLEDs applications is from 10uH to 33uH. Small size and better efficiency are the major concerns for portable devices, such as the RT9292 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 RT9292 applications for driving 6 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 DS9292-02 April 2011 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 JAis the junction to ambient thermal resistance. For recommended operating conditions specification of RT9292, 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 WDFN8L 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 The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance JA. For RT9292 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 Maximum Power Dissipation (W) Current Limiting Single Layer PCB 0.7 WDFN-8L 2x2 0.6 0.5 TSOT-23-6 0.4 0.3 0.2 0.1 0 0 25 50 75 100 125 Ambient Temperature (C) Figure 6. Derating Curves for RT9292 Packages www.richtek.com 11 RT9292 Layout Consideration For best performance of the RT9292, 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. 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. VIN L GND C IN should be placed as closed as possible to VIN pin for good filtering. C IN LX 1 6 VIN GND 2 5 VOUT 3 4 EN C OUT R SET FB WLEDs 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. The C OUT should be connected directly from the Pin 5 to ground rather than across the LEDs Figure 7. Layout Consideration Recommended www.richtek.com 12 DS9292-02 April 2011 RT9292 Outline Dimension H D L C B b A A1 e Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.700 1.000 0.028 0.039 A1 0.000 0.100 0.000 0.004 B 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 C 2.591 3.000 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024 TSOT-23-6 Surface Mount Package DS9292-02 April 2011 www.richtek.com 13 RT9292 D2 D L E E2 1 e SEE DETAIL A b 2 1 2 1 A A1 A3 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. Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.200 0.300 0.008 0.012 D 1.950 2.050 0.077 0.081 D2 1.000 1.250 0.039 0.049 E 1.950 2.050 0.077 0.081 E2 0.400 0.650 0.016 0.026 e L 0.500 0.300 0.020 0.400 0.012 0.016 W-Type 8L DFN 2x2 Package Richtek Technology Corporation Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 5F, No. 95, Minchiuan Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)86672399 Fax: (8862)86672377 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. www.richtek.com 14 DS9292-02 April 2011