RT4526GJ6

® RT4526 Small Package, High Performance, Asynchronous Boost LED Driver General Description Features The RT4526 is a high frequency, asynchronous Boost converter. The internal MOSFET can support up to 10 white LEDs for backlighting and OLED power applications, and 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. For the protection, the RT4526 provides 37V OVP to allow inexpensive and smalloutput capacitors with lower voltage ratings. The LED current is initially set with the external sense resistor RSET. The RT4526 is available in the tiny TSOT-23-6 package to provide the best solution for PCB space saving and total BOM cost.           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 RoHS Compliant and Halogen Free Applications   Ordering Information  RT4526  Package Type J6 : TSOT-23-6 Cellular Phones Digital Cameras PDAs and Smart Phones and MP3 and OLED. Portable Instruments Pin Configurations Lead Plating System G : Green (Halogen Free and Pb Free) (TOP VIEW) Note : VIN VOUT EN Richtek products are :  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. 5 4 2 3 LX GND FB TSOT-23-6 Simplified Application Circuit D L LX VIN VIN CIN Enable VOUT VOUT COUT RT4526 EN GND 8 WLEDs FB RSET Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4526-02 March 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT4526 Marking Information 06= : Product Code 06=DNN DNN : Date Code Functional Pin Description Pin No. Pin Name Pin Function 1 LX Switch Node. Open-drain output of the internal N-MOSFET. Connect this pin to external inductor and diode. 2 GND Ground. 3 FB Feedback Voltage Input. Connect a resistor to GND to set output current. 4 EN Enable Control Input (Active High). 5 VOUT Output Voltage. (For OVP detect function) 6 VIN Supply Input. Function Block Diagram VIN UVLO OTP Logic Control, Minimum On Time PWM CurrentSense LX + + EA GM Driver GND + - Slope Compensation LPF Enable Logic Shutdown 20ms 1µA FB PWM Oscillator Reference Voltage VREF Bias Current EN Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 VOUT OCP Internal Compensation Internal Soft-Start OVP is a registered trademark of Richtek Technology Corporation. DS4526-02 March 2015 RT4526 Operation The RT4526 is an asynchronous step-up converter that can support input voltage from 2.5V to 5.5V. When the power plugs in and EN = H, VOUT is soft-started (20m sec) to avoid the inrush current of VIN. Normally, the low-side MOSFET is turned on by logic control which drives the gate driver block when VFB is lower than the internal reference voltage. The low-side MOSFET will be turned on by minimum on-time. When the low-side MOSFET is turned off, the current of inductor provide the power to VOUT until VFB is lower than the internal reference voltage. Then, the low-side MOSFET is turned on. When the current of low-side MOSFET is over the rating current, the lowside MOSFET is turned off. When the temperature is over the rating temperature, the low-side MOSFET is turned off until the temperature is dropped by the OTP block. When VIN is lower than 2.1V, the low-side MOSFET is turned off by the UVLO block. When VOUT is higher than rating voltage, the low-side MOSFET is turned off by the OVP block. Internal clock is proved by the PWM Oscillator block. Internal reference voltage is provided by the Reference Voltage block. Internal current bias is provided by the Bias Current block. the EN pin is pulled low by 1μA current source. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4526-02 March 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT4526 Absolute Maximum Ratings           (Note 1) Supply Input Voltage, VIN -----------------------------------------------------------------------------------------------Switching Pin, LX ---------------------------------------------------------------------------------------------------------VOUT ------------------------------------------------------------------------------------------------------------------------Other Pins ------------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C −0.3V to 6V −0.3V to 50V −0.3V to 46V −0.3V to 6V TSOT-23-6 ------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) TSOT-23-6, θJA ------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------------- 0.5W Recommended Operating Conditions   197.4°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 3.7V, CIN = 2.2μF, COUT = 0.47μF, IOUT = 20mA, L = 22μH, TA = 25°C, unless otherwise specified) Parameter Symbol Input Voltage VIN Under-Voltage Lockout VUVLO Test Conditions UVLO Hysteresis Min Typ Max Unit 2.5 -- 5.5 V 2 2.2 2.45 V -- 0.1 -- V Quiescent Current IQ FB = 1.5V, No Switching -- 400 600 A Supply Current IIN FB = 0V, Switching -- 1 2 mA Shutdown Current ISHDN VEN < 0.4V -- 1 4 A Line Regulation VIN = 3V to 4.3V -- 1 -- % Load Regulation 1mA to 20mA -- 1 -- % 0.75 1 1.25 MHz Maximum Duty Cycle 90 92 -- % Clock Rate 0.1 -- 200 kHz 285 300 315 mV -- 0.7 1.2  Operation Frequency fOSC Feedback Reference Voltage VREF On Resistance RDS(ON) EN Threshold Voltage Logic-High VIH 1.4 -- -- Logic-Low VIL -- -- 0.5 IIH -- 1 -- A -- 0.1 -- V EN Sink Current EN Hysteresis V Over Voltage Threshold VOVP 35 37 39 V Over Current Threshold IOCP 1 1.2 -- A Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS4526-02 March 2015 RT4526 Parameter OTP Symbol Test Conditions TOTP OTP Hysteresis Shutdown Delay TSHDN Min Typ Max Unit -- 160 -- C -- 30 -- C -- 20 -- ms Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and 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 may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4526-02 March 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT4526 Typical Application Circuit L 22µH to 47µH D VOUT 1 VOUT 5 COUT 1µF 6 VIN VIN CIN 2.2µF Enable LX RT4526 4 EN 2 GND 8 WLEDs FB 3 RSET Note : The IC is not suitable for unstable supply applications which caused by the external components of VIN. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS4526-02 March 2015 RT4526 Typical Operating Characteristics Efficiency vs. Input Voltage Efficiency vs. Output Current 100 100 VIN = 4.5V 80 80 VIN = 4V Efficiency (%) 70 Efficiency (%) ILOAD = 30mA 90 90 60 50 40 30 20 ILOAD = 10mA 70 ILOAD = 20mA 60 50 40 30 20 10 10 VOUT = 10V VOUT = 34V 0 0 0 0.05 0.1 0.15 0.2 0.25 0.3 2.5 3 3.5 Output Current (A) 4.5 5 Quiescent Current vs. Input Voltage 500 35 450 Quiescent Current (µA) 40 30 25 20 15 400 350 300 250 VFB = 1.5V VIN = 3.7V, VOUT = 34V 200 10 5 15 25 35 45 55 65 75 2.5 85 3 3.5 4 4.5 5 5.5 Input Voltage (V) Output Current (mA) Frequency vs. Temperature Frequency vs. Input Voltage 1100 1100 1050 1050 Frequency (kHz) Frequency (kHz) 5.5 Input Voltage (V) Output Voltage vs. Output Current Output Voltage (V) 4 1000 950 900 1000 950 900 850 850 VIN = 3.7V, ILED = 20mA ILED = 20mA 800 800 2.5 3 3.5 4 4.5 5 Input Voltage (V) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4526-02 March 2015 5.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT4526 Reference Voltage vs. Input Voltage Reference Voltage vs. Temperature 0.32 0.34 Reference Voltage (V) Reference Voltage (V) 0.33 0.29 VOUT = 34V, IOUT = No Load 0.26 10WLED, ILED = 20mA 0.23 0.2 0.32 VIN = 3V 0.31 VIN = 3.7V 0.30 VIN = 4.2V 0.29 0.28 0.27 ILED = 20mA 0.17 0.26 2.5 3 3.5 4 4.5 5 5.5 -40 -15 35 60 85 Temperature (°C) Input Voltage (V) Reference Voltage vs. Output Current Enable Threshold vs. Input Voltage 1.00 0.314 0.98 VIN = 3V 0.310 Rising 0.96 0.306 VIN = 4.2V VIN = 3.7V 0.302 0.298 Enable Voltage (V) Reference Voltage (V) 10 0.94 0.92 0.90 0.88 Falling 0.86 0.84 0.294 VOUT = 34V 0.82 0.80 0.290 0 5 10 15 20 25 30 2.5 3 3.5 4 4.5 Output Current (mA) Input Voltage (V) LED Current vs. Duty Power On from EN 5 5.5 25 LED Current (mA) 20 VEN (2V/Div) 15 f f f f 10 = 200Hz = 2kHz = 20kHz = 200kHz 5 VOUT (10V/Div) 6WLED, ILED = 20mA, VIN = 3.7V VIN = 3.7V, ILED = 20mA 0 0 10 20 30 40 50 60 70 80 90 100 Time (1ms/Div) Duty (%) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS4526-02 March 2015 RT4526 Power Off from EN Ripple Voltage VIN (20mV/Div) VEN (2V/Div) VOUT (20mV/Div) VOUT (10V/Div) VIN = 3.7V, ILED = 20mA VIN = 3.7V, ILED = 20mA Time (1ms/Div) Time (500ns/Div) PWM Dimming from EN PWM Dimming from EN f = 20kHz f = 200Hz VEN (4V/Div) VEN (4V/Div) I LED (10mA/Div) I LED (10mA/Div) VIN = 3.7V, ILED = 20mA Time (1ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4526-02 March 2015 VIN = 3.7V, ILED = 20mA Time (10μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT4526 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 the 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 300mV EN VA For the brightness dimming control of the RT4526, the IC provides typically 300mV feedback voltage when the EN pin is pulled constantly high. However, the 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 the 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 than 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 approaches a DC signal. The LED current is a DC current which eliminates 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. To Controller FB Figure 1. Block Diagram of Programmable FB Voltage Using PWM Signal PWM Minimum Duty Dimming Control a. Using a PWM Signal to EN Pin + EA - Dimming frequency < 500Hz 4% Dimming frequency > 500Hz 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 which is shown in Figure 2. As the DC voltage increases, the current flows through R3 increasingly and the voltage drop on R3 increases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2.8V and assume the RT4526 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. R3  (VDC  VREF ) VREF  R4 ILED = RSET VIN 2.5V to 5.5V VOUT L 10µH to 47µH D COUT 1µF CIN 2.2µF RT4526 6 VIN 2 3 GND FB LX 1 VOUT EN 5 4 WLEDs Enable R3 10k R4 85k RSET 16 VDC Dimming 0V to 2.8V Figure 2. Dimming Control Using a DC Voltage For the RT4526, the minimum duty vs. frequency is listed in following table. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS4526-02 March 2015 RT4526 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 (10k R2 D COUT 1µF CIN 2.2µF RT4526 6 2 3 VIN GND LX 1 VOUT EN FB COUT 1µF CIN 2.2µF RT4526 5 WLEDs 4 2 Enable 3 R4 3k RDC 82k LX 1 6 VIN R3 10k GND VOUT EN FB 5 R1 4 Enable RSET 16 CDC 1µF R2 2.8V 0V PWM Signal Figure 5. Constant Output Voltage Application Figure 3. Dimming Control Using a Filtered PWM Signal VIN 20 VOUT L 22µH D 18 COUT 1µF CIN 2.2µF 16 LED Current (mA) VOUT L 10µH to 47µH 14 RT4526 6 12 1 VIN LX 2 GND VOUT 5 … 10 Enable 4 EN 8 FB 3 3 x 13 WLEDs 6 4 RSET 2 0 0 20 40 60 80 100 Figure 6. Application for Driving 3 X 13 WLEDs PWM Duty (%) Figure 4. PWM Duty Cycle vs. LED Current Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4526-02 March 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT4526 Application for Driving 3 x 13 WLEDs Inductor Selection The RT4526 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 the following equation. The recommended value of inductor for 10 WLEDs applications is from 10μH to 47μH. Small size and better efficiency are the major concerns for portable devices, such as the RT4526 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. ITotal = VREF RSET 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 RT4526 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 flows through inductor during charging period is detected by a current sensing circuit. As the value comes across the current limiting threshold, the NMOSFET 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 (OVP) is detected by a junction breakdown detecting circuit. Once VOUT goes over the detecting voltage, the 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 160°C, the chip will also enter protection mode. The power MOSFET will be turned off during protection mode to prevent abnormal operation. Capacitor Selection A 2.2μF input ceramic capacitor and a 1μF output ceramic capacitor are recommended for the RT4526 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 ) / θJA Where T J(MAX) is the maximum operation junction temperature, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. Where T J(MAX) is the maximum operation junction temperature, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. For the recommended operating conditions specification of RT4526, the maximum junction temperature of the die is 125°C. The junction to ambient thermal resistance θJA is layout dependent. For TSOT-23-6 package, the thermal resistance, θJA, is 197.4°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by following formula : PD(MAX) = (125°C − 25°C) / (197.4°C/W) = 0.5W for TSOT-23-6 package Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS4526-02 March 2015 RT4526 The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 7 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Maximum Power Dissipation (W)1 0.6 Layout Consideration For best performance of the RT4526, 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 should be connected to a strong ground plane for heat sinking and noise protection.  Keep the main current traces as short and wide as possible .  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. Four-Layer PCB 0.5 0.4 0.3 0.2 0.1 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 7. Derating Curve of Maximum Power Dissipation 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 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 close as possible to VIN pin for good filtering. D L LX 1 6 VIN GND 2 5 VOUT 3 4 EN CIN RSET 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. Figure 8. PCB Layout Guide Table 1. Recommended Components for Typical Application Circuit Reference Qty Part Number Description D 1 SR26 CIN 1 EMK107BJ225MA-T Capacitor, Ceramic, 2.2F/16V X5R Taiyo Yuden COUT 1 GMK107BJ105KA Capacitor, Ceramic, 1F/50V X5R Taiyo Yuden RSET 1 RC0603FR Resistor 15, 1% YAGEO L 1 NR4018T220M Inductor, 22H Taiyo Yuden Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4526-02 March 2015 Schottky Diode Manufacture PANJIT is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT4526 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 Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. www.richtek.com 14 DS4526-02 March 2015