® RT9278 High Efficiency Boost LDO Converter & High Power White LED Driver General Description Features The RT9278 is a compact, high efficiency, synchronous step-up converter, it provides a power supply solution for products powered by either two-cell, three-cell Alkaline/ NiMH or one-cell Li-Ion/Li-polymer battery. The RT9278 is boost converter with PWM control loop, provide up to 95% efficiency by using a synchronous rectifier. The maximum peak current in the internal switch is limited to up to 2A. It keeps the output voltage regulated when the input voltage exceeds the setting output voltage. The output voltage can be set by an external resister divider, or be fixed to reduce external components. It integrates a linear controller for linear regulator. 95% Efficiency Synchronous Boost Converter High Supply Capability 2A Current Limit Input Voltage Range : 1.5V to 5.5V 600kHz Fixed Switching Rate Adjustable Output Voltage Options Up to 5.5V Output Voltage Keep Regulated when Input Voltage Exceed Setting Output Voltage 1uA Supply Current in Shutdown Mode External Compensation Network Build in Linear Controller for Linear Regulator Over Temperature Protection Small 10-Lead VDFN Package RoHS Compliant and 100% Lead (Pb)-Free RT9278 is available in VDFN-10L 3x3 package. Applications Ordering Information RT9278 Package Type QV : VDFN-10L 3x3 (V-Type) Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) Digital Still Camera Camera White LED Flash Light PDAs Portable Device Marking Information RT9278PQV Note : AC- : Product Code Richtek products are : ` RoHS compliant and compatible with the current require- ` Suitable for use in SnPb or Pb-free soldering processes. AC-YM DNN YMDNN : Date Code ments of IPC/JEDEC J-STD-020. RT9278QQV Pin Configurations AC= : Product Code AC=YM DNN (TOP VIEW) 1 10 2 9 3 GND 5 8 7 4 11 9 FB COMP GND EN LX YMDNN : Date Code LFB LDRI PGND VDD VOUT VDFN-10L 3x3 Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9278-07 January 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT9278 Typical Application Circuit Chip Enable L1 1 to 10µH VIN 4 EN Chip Shutdown 100ms 5 LX 8 C1 4.7µF R1 2.2k VDD 7 RT9278 PGND 2 COMP 3 GND C2 12nF C3 1µF Q1 AO7401 VOUT 6 C4 2.2µF FB 1 LDRI 9 LFB 10 700mA 100ms D1 Power LED R2 300k R3 0.28 Figure 1. Novel Up-Down Driver for Power LED with Strobe Mode Note : Patent Pending. VIN Chip Enable 4 EN VDD 7 L1 RT9278 Chip Shutdown 1 to 10µH 5 LX VOUT 6 8 C1 PGND 4.7µF FB 1 R1 2.2k 2 COMP LDRI 9 3 GND LFB 10 C2 12nF Istrobe C3 1µF Q1 AO3403 C4 2.2µF IMovie 700mA 2.8V GPIO R2 300k 200mA 100ms 0V D1 Power LED R4 1k R3 0.28 R5 18.2k R4 = 1kΩ R3 = 0.2 IStrobe (GPIO_HI − 0.2) x R4 R5 = 0.2 − (IMovie x R3) GPIO Figure 2. Novel Up-Down Driver for Power LED with Strobe Mode and Movie Mode Note : Patent Pending. The GPIO Signal has to pull high before enable IC. Chip Enable L1 4.7uH 4 Chip Shutdown VIN R1 2.5k C1 10µF C2 2.2nF VDD 7 EN RT9278 5 LX 6 2 COMP VOUT 8 PGND 9 10 LFB LDRI 1 3 GND FB C3 1µF C4 10µF Q1 AO3403 R2 510k C5 100pF VOUT 3.3V R3 470k R4 150k Figure 3. Synchronous Boost Converter with Load Disconnect in Shutdown Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS9278-07 January 2012 RT9278 VIN 1.6V to 5V L1 4.7µH 4 EN GPIO 5 LX 8 C1 10µF R1 51k VDD 7 RT9278 PGND 2 COMP 3 GND C2 3.3nF C3 1µF VOUT 6 Q1 AO3403 C4 10pF FB 1 R2 732k C5 20µF R5 620k R4 510k R3 226k VOUT 3.3V LDRI 9 10 LFB C6 22pF C7 1µF R6 40.2k Figure 4. Boost-LDO Application for Constant Output Voltage VIN 1.6V to 3.0V L1 4.7µH GPIO 4 EN 5 LX 8 C1 20µF R1 3.9k C2 1.5nF VDD 7 RT9278 PGND 2 COMP 3 GND VOUT 6 FB 1 VOUT1 3.3V/300mA C3 1µF C4 10pF Q1 AO3403 R2 470k C5 40µF R3 150k R5 887k R4 510k LDRI 9 10 LFB C6 22pF VOUT2 1.8V/150mA C7 30µF R6 110k Figure 5. Synchronous Boost Converter Driver for Dual Output Voltage Chip Enable L VIN Chip Shutdown C1 10µF RCOMP CCOMP 4 EN VDD 7 RT9278 5 LX 9 LDRI 10 LFB 2 COMP 3 GND C3 1µF VOUT PVD CFF FB 1 PGND 8 R2 COUT 40µF R1 Figure 6. Synchronous Boost Converter Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9278-07 January 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT9278 Table 1. Component Selection for Figure 6 (L=2.2µH) Input Voltage Output Voltage (V) (V) L (µH) COUT (µF) R1 (kΩ) R2 (kΩ) RCOMP (kΩ) CCOMP (nF) CFF (pF) 1.5~3.0 3.3 2.2 40 150 470 43 5.6 18 1.5~3.3 5.0 2.2 40 130 680 24 8.2 12 3.0~4.5 5.0 2.2 40 130 680 24 3.9 12 Table 2. Component Selection for Figure 6 (L=4.7µH) Input Voltage Output Voltage (V) (V) L (µH) COUT (µF) R1 (kΩ) R2 (kΩ) RCOMP (kΩ) CCOMP (nF) CFF (pF) 1.5~3.0 3.3 4.7 40 150 470 24 10 18 1.5~3.3 5.0 4.7 40 130 680 24 15 12 3.0~4.5 5.0 4.7 40 130 680 24 8.2 12 Table 3. Component Selection for Figure 6 (L=6.8µH) Input Voltage Output Voltage (V) (V) L (µH) COUT (µF) R1 (kΩ) R2 (kΩ) RCOMP (kΩ) CCOMP (nF) CFF (pF) 1.5~3.0 3.3 6.8 40 150 470 24 15 18 1.5~3.3 5.0 6.8 40 130 680 24 22 12 3.0~4.5 5.0 6.8 40 130 680 24 12 12 Table 4. Component Selection for Figure 6 (L=10µH) Input Voltage Output Voltage (V) (V) L (µH) COUT (µF) R1 (kΩ) R2 (kΩ) RCOMP (kΩ) CCOMP (nF) CFF (pF) 1.5~3.0 3.3 10 40 150 470 24 22 18 1.5~3.3 5.0 10 40 130 680 24 33 12 3.0~4.5 5.0 10 40 130 680 24 18 12 Copyright ©2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS9278-07 January 2012 RT9278 Functional Pin Description Pin No. Pin Name Pin Function 1 FB Feedback Input Pin. 2 COMP Feedback Compensation Pin. 3 GND Ground. 4 EN Enable Input Pin 5 LX Switch Node. 6 VOUT Output Pin 7 VDD Device Input Power Pin. 8 PGND Power Ground. 9 LDRI Linear Controller Driver Output. 10 LFB Linear Controller Feedback Input. The exposed pad must be soldered to a large PCB and connected to 11 (Exposed Pad) GND GND for maximum power dissipation. Function Block Diagram COMP VOUT Error AMPLIFIER - FB VREF = 0.8V Error Comparator - + + VDD Control and Driver Logic LX GND Oscillator and Shutdown Control EN Slope Compensation Current Sense PGND LDRI LFB VREF = 0.2V + Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9278-07 January 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT9278 Operation RT9278 integrates a high-efficiency step-up DC-DC converter and a linear regulator controller. The boost converter is based on a fixed frequency, pulse-width-modulation (PWM) controller using a synchronous rectifier to obtain maximum efficiency. Current mode control with external compensation network makes it easy to stabilize the system and keep maximum flexibility. The linear regulator controller can use to drive the external P-Channel MOSFET switch for load disconnection. It keeps the output voltage regulated even when the input voltage exceeds the nominal output voltage, and keeps the output voltage completely disconnected from input voltage (battery) when the chip is in shutdown mode Soft-start When the chip is enabled. Soft-start is achieved by ramping up the PWM duty from very small to normal operation. The ramping up PWM duty is achieved by sourcing 1uA from error amplifier to the compensation capacitor. When the output voltage is regulated, the PWM duty enters the normal operation, and the error amplifier can sink and source up to 22uA. The soft-start time is set by the following formula : TSS = (1V - 1μA x RCOMP) x CCOMP 1μA RCOMP and CCOMP are compensation components. Current limit The current of NMOS is sensed cycle by cycle to prevent over current. When over current limit, then the NMOS is off. This state is latched and then reset automatically at next clock cycle. Over voltage When the chip voltage is higher than 6.5V, Switch is off. When the Over Voltage Protection is relieved, the chip operates well again. Thermal protection Thermal protection function is integrated in the chip. When the chip temperature is higher than 180°C, the controllers are shutdown. 20°C is the hysteresis range of temperature to prevent unstable operation when the thermal protection happens. When the thermal protection is relieved, the chip operates well again. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS9278-07 January 2012 RT9278 Absolute Maximum Ratings z z z z z z z z z (Note 1) Supply Voltage, VDD -------------------------------------------------------------------------------------------------- 7V LX Pin Voltage ---------------------------------------------------------------------------------------------------------- − 0.3V to 7V The Other pins --------------------------------------------------------------------------------------------------------- − 0.3V to 7V Power Dissipation, PD @ TA = 25°C VDFN-10L 3x3 ---------------------------------------------------------------------------------------------------------- 1.43W Package Thermal Resistance (Note 2) VDFN-10L 3x3, θJA ---------------------------------------------------------------------------------------------------- 70°C/W Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C Junction Temperature ------------------------------------------------------------------------------------------------- 150°C Storage Temperature Range ---------------------------------------------------------------------------------------- − 65°C to 150°C ESD Susceptibility (Note 3) HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 2kV Recommended Operating Conditions z z (Note 4) Ambient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C Junction Temperature Range ---------------------------------------------------------------------------------------- −40°C to 125°C Electrical Characteristics (VBAT = 1.8V, VOUT = 3.3V, TA = 25°C, unless otherwise specified) Parameter Min Typ Max Unit -- 1.5 -- V Operating Voltage Range, After start-up VBAT 1.1 -- 5.5 V VOUT Output Voltage Range 2.4 -- 5.5 V -- 6.5 -- V Start-Up Voltage Symbol VST Test Conditions IL = 1mA VOUT_ADJ VOUT Over Voltage Protection Switch-off Current I (VBAT) I SW OFF VOUT = 3.3V, VFB = 0.9V -- 200 350 μA Shutdown Current I OFF EN Pin = 0V, Open Loop -- 0.01 1 μA Feedback Reference Voltage VFB Close Loop, VOUT = 3.3V 0.784 0.8 0.816 V Switching Frequency fS -- 650 -- kHz Maximum Duty D(MAX) -- 85 -- % SWN Switch ON Resistance VOUT = 3.3V -- 210 -- mΩ SWP Switch ON Resistance VOUT = 3.3V -- 240 -- mΩ VOUT = 3.3V -- 2 -- A GM -- 0.2 -- ms Compensation Source Current -- 22 -- μA Compensation Sink Current -- 22 -- μA Current Limit Setting I SW Error Amplifier Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9278-07 January 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT9278 Parameter Symbol Test Conditions Min Typ Max Unit -- 0.2 -- V EN Input High Level Threshold -- -- 1.3 V EN Input Low Level Threshold 0.4 -- -- V Linear Controller Feedback Voltage for Linear Controller VLFB Thermal Shutdown T SD -- 180 -- °C Thermal Shutdown Hysteresis ΔTSD -- 20 -- °C 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 © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS9278-07 January 2012 RT9278 Typical Operating Characteristics Frequency vs. Temperature 700 Reference Voltage vs. Temperature 0.804 VDD = 3.3V VDD = 3.3V 0.803 Reference Voltage (V) 660 640 620 600 0.802 0.801 0.8 0.799 0.798 0.797 580 0.796 -50 -25 0 25 50 75 100 125 -50 -25 Efficiency vs. Output Current Efficiency (%) VIN VIN VIN VIN 70 60 = = = = 3.0V 2.5V 2.0V 1.5V 50 40 30 20 10 100 125 VOUT = 5V 70 VIN VIN VIN VIN VIN VIN VIN 60 50 40 30 = = = = = = = 4.5V 4.0V 3.5V 3.0V 2.5V 2.0V 1.5V 20 10 0 1 10 100 1000 1 10 100 1000 Output Current (mA) Output Current (mA) Input Voltage vs. Output Voltage Input Voltage vs. Output Voltage 5.150 VOUT = 3.3V VOUT = 5V 5.100 Output Voltage (V) 3.325 Output Voltage (V) 75 80 0 3.350 50 90 Efficiency (%) VOUT = 3.3V 90 80 25 Efficiency vs. Output Current 100 Refer to Application Circuit Figure 3 100 0 Temperature (°C) Temperature (°C) Refer to Application Circuit Figure 3 Frequency (kHz) 680 3.300 3.275 3.250 5.050 5.000 4.950 4.900 3.225 4.850 3.200 1.6 1.8 2.0 2.2 2.4 2.6 2.8 Input Voltage (V) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9278-07 January 2012 3.0 1.6 1.925 1.93 2.25 2.575 2.58 2.9 3.225 3.23 3.55 3.875 3.88 4.2 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT9278 Output Voltage vs. Output Current Output Voltage vs. Output Current 3.310 4.98 4.97 4.96 3.305 3.295 Output Voltage (V) Output Voltage (V) 3.300 3.290 3.285 3.280 3.275 3.270 VIN VIN VIN VIN 3.265 3.260 3.255 = = = = 3.0V 2.5V 2.0V 1.5V VOUT = 3.3V 1 10 100 4.88 4.87 4.86 VIN VIN VIN VIN VIN VIN VIN VOUT = 5V 1 1000 = = = = = = = 4.2V 4.0V 3.5V 3.0V 2.5V 2.0V 1.5V 10 100 Output Current (mA) Power LED Efficiency vs. Input Voltage Normal Operation 90 80 70 60 50 40 30 20 Vf = 3.5V, ILED = 200mA, L = 4.7μH Refer to Application Circuit Figure 1 Output Current (mA) 100 Power LED Efficiency (%) 4.92 4.91 4.90 4.89 4.85 3.250 10 4.95 4.94 4.93 1000 VOUT (10mV/Div) (5V/Div) VLX (1V/Div) VIN I IN (500mA/Div) VIN = 1.5V, VOUT = 5V, ILOAD = 100mA 0 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3 Time (1μs/Div) Input Voltage (V) Normal Operation Normal Operation VOUT VOUT (10mV/Div) (10mV/Div) (5V/Div) VIN (1V/Div) VLX VLX (1V/Div) VIN I IN (1A/Div) I IN VIN = 1.5V, VOUT = 5V, ILOAD = 300mA Time (1μs/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 (5V/Div) (500mA/Div) VIN = 4.2V, VOUT = 5V, ILOAD = 100mA Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. DS9278-07 January 2012 RT9278 Normal Operation Load Transient Regulation VIN = 1.5V, VOUT = 5V, ILOAD = 100mA to 300mA Load Current (mA) (10mV/Div) VOUT VIN (1V/Div) VLX 400 200 0 I IN (500mA/Div) VIN = 4.2V, VOUT = 5V, ILOAD = 300mA Output Voltage Deviation (mV) (5V/Div) 50 0 -50 Time (1μs/Div) Time (1ms/Div) Load Transient Regulation Flash LED Load Current (mA) VIN = 4.2V, VOUT = 5V, ILOAD = 100mA to 400mA VIN = 3.0V, Power LED = 200mA to 700mA VIN 400 200 (100mV/Div) 0 (2V/Div) Output Voltage Deviation (mV) GPIO (500mA /Div) 100 0 I LED -100 I IN (500mA/Div) Time (1ms/Div) Time (10ms/Div) Flash LED Flash LED VIN = 3.77V, Power LED = 200mA to 700mA VIN VIN = 4.3V, Power LED = 200mA to 700mA VIN (100mV/Div) (100mV/Div) (2V/Div) (2V/Div) GPIO GPIO (500mA /Div) (500mA/Div) I LED I LED I IN (500mA/Div) Mode Transition Time (10ms/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS9278-07 January 2012 I IN (500mA/Div) Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT9278 Application Information RT9278 integrates a high-efficiency synchronous rectifier step-up DC-DC converter and a linear regulator controller. To fully utilize its advantages, peripheral components should be appropriately selected. The following information provides basic considerations for component selection. Inductor Selection For a better efficiency in high switching frequency converter, the inductor selection has to use a proper core material such as ferrite core to reduce the core loss and choose low ESR wire to reduce copper loss. The most important point is to prevent the core saturated when handling the maximum peak current. Using a shielded inductor can minimize radiated noise in sensitive applications. The maximum peak inductor current is the maximum input current plus the half of inductor ripple current. The calculated peak current has to be smaller than the current limitation in the electrical characteristics. A typical setting of the inductor ripple current is 20% to 40% of the maximum input current. If the selection is 40% 1 IPK = IIN(MAX) + IRIPPLE = 1.2 × IIN(MAX) 2 ⎡ (IOUT(MAX) × VOUT ⎤ = 1.2 × ⎢ ⎥ ⎣⎢ η × VIN(MIN) ⎦⎥ The minimum inductance value is derived from the following equation : L= η × IIN(MIN)2 × [VOUT - VIN(MIN) ] 0.4 × IOUT(MAX) × VOUT 2 × fOSC Depending on the application, the recommended inductor value is between 2.2μH and 10μH. as well, but the ESR is bigger than ceramic capacitor. The output voltage ripple consists of two components: one is the pulsating output ripple current flows through the ESR, and the other is the capacitive ripple caused by charging and discharging. VRIPPLE = VRIPPLE(ESR) + VRIPPLE(C) ≅ IPEAK × ESRC OUT + Output Voltage Setting Referring to application circuits (Figure 6), the output voltage of the switching regulator (VOUT) can be set with below equation : R2 ) × VFB, VOUT = (1 + R1 VFB = 0.8V (typ.) Linear Regulator Linear Regular MOSFETs Selection The linear controller of RT9278 was designed to drive an external P-Channel MOSFET. The main consideration of pass MOSFETs of linear regulator is package selection for efficient removal of heat. The power dissipation of a linear regulator is Plinear = (VIN − VOUT) x IOUT For better input bypassing, low-ESR ceramic capacitors are recommended for performance. A 10μF input capacitor is sufficient for most applications. For a lower output power requirement application, this value can be decreased. Layout Consideration ` ` Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 A full GND plane without gap break. VDD to GND noise bypass − Short and wide connection for the 1μF MLCC capacitor between Pin7 and Pin3. VIN to GND noise bypass − Add a capacitor close to L1 inductor, when VIN is not an ideal voltage source. ` Minimized FB node copper area and keep far away from noise sources. ` The MOSFETs of linear regulator should have wide pad to dissipate the heat. Output Capacitor Selection For lower output voltage ripple, low-ESR ceramic capacitors are recommended. The tantalum capacitors can be used (W) The criterion for selection of package is the junction temperature below the maximum desired temperature with the maximum expected ambient temperature. ` Input Capacitor Selection IPP 2×C× f is a registered trademark of Richtek Technology Corporation. DS9278-07 January 2012 RT9278 Outline Dimension 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 0.800 1.000 0.031 0.039 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 2.950 3.050 0.116 0.120 D2 2.300 2.650 0.091 0.104 E 2.950 3.050 0.116 0.120 E2 1.500 1.750 0.059 0.069 e L 0.500 0.350 0.020 0.450 0.014 0.018 V-Type 10L DFN 3x3 Package Richtek Technology Corporation 5F, No. 20, Taiyuen 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. DS9278-07 January 2012 www.richtek.com 13