RT9278 Preliminary 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. l 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. l l l l l l l 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. l l l l l 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 1µA 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 l RT9278 l Package Type QV : VDFN-10L 3x3 (V-Type) Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) l l Digital Still Camera Camera White LED Flash Light PDAs Portable Device Pin Configurations (TOP VIEW) Note : }RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. }Suitable for use in SnPb or Pb-free soldering processes. }100% matte tin (Sn) plating. FB COMP GND EN LX 1 10 2 9 3 GND 5 8 7 4 11 9 Richtek Pb-free and Green products are : LFB LDRI PGND VDD VOUT VDFN-10L 3x3 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. DS9278-04 August 2007 www.richtek.com 1 RT9278 Preliminary Typical Application Circuit Chip Enable 4 EN Chip Shutdown 100ms L1 1 to 10uH VIN 5 LX 8 C1 4.7uF R1 2.2k VDD 7 RT9278 Q1 AO7401 VOUT 6 PGND 2 COMP 3 GND C2 12nF C3 1uF C4 2.2uF 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. Chip Enable 4 L1 1 to 10uH Chip Shutdown VIN 5 LX 8 C1 4.7uF R1 2.2k C2 12nF EN VDD 7 RT9278 Istrobe C3 1uF Q1 AO3403 VOUT 6 PGND 2 COMP 3 GND C4 2.2uF 1 FB LDRI 9 LFB 10 IMovie 700mA 2.8V GPIO R2 300k 200mA 100ms 0V D1 Power LED R4 1k R3 0.28 R5 18.2k GPIO R4 = 1kΩ 0.2 R3 = IStrobe (GPIO_HI − 0.2) x R4 R5 = 0.2 − (IMovie x R3) Figure 2. Novel Up-Down Driver for Power LED with Strobe Mode and Movie Mode Note : l Patent Pending. l The GPIO Signal has to pull high before enable IC. Chip Enable L1 4.7uH 4 Chip Shutdown VIN R1 2.5k C1 10uF C2 2.2nF VDD 7 EN RT9278 5 LX 6 2 COMP VOUT 8 PGND 9 10 LDRI LFB 1 3 FB GND C3 1uF C4 10uF Q1 AO3403 R2 510k VOUT 3.3V C5 100pF R3 470k R4 150k Figure 3. Synchronous Boost Converter with Load Disconnect in Shutdown www.richtek.com 2 DS9278-04 August 2007 RT9278 Preliminary VIN 1.6V to 5V L1 4.7uH 4 EN GPIO 5 LX 8 C1 10uF R1 51k VDD 7 RT9278 C3 1uF PGND FB 1 2 COMP C4 10pF R2 732k C5 20uF VOUT 3.3V R5 620k R4 510k R3 226k 3 GND C2 3.3nF Q1 AO3403 VOUT 6 LDRI 9 10 LFB C6 22pF C7 1uF R6 40.2k Figure 4. Boost-LDO Application for Constant Output Voltage VIN 1.6V to 3.0V L1 4.7uH GPIO 4 EN 5 LX 8 C1 20uF R1 3.9k C2 1.5nF VDD 7 RT9278 VOUT1 3.3V/300mA C3 1uF Q1 AO3403 VOUT 6 PGND 2 COMP 3 GND FB 1 C4 10pF R2 470k C5 40uF R3 150k VOUT2 1.8V/150mA R5 887k R4 510k LDRI 9 10 LFB C6 22pF C7 30uF R6 110k Figure 5. Synchronous Boost Converter Driver for Dual Output Voltage Chip Enable L Chip Shutdown 4 EN VDD 7 RT9278 5 LX 9 LDRI VIN C1 10uF CCOMP VOUT PVD 10 LFB RCOMP C3 1uF CFF 2 COMP 1 FB 3 GND PGND 8 R2 C OUT 40uF R1 Figure 6. Synchronous Boost Converter DS9278-04 August 2007 www.richtek.com 3 RT9278 Preliminary 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) C FF (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) C FF (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) C FF (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 www.richtek.com 4 DS9278-04 August 2007 RT9278 Preliminary 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 Exposed Pad (11) GND GND for maximum power dissipation. Function Block Diagram COMP Error AMPLIFIER - FB VREF = 0.8V + VOUT Error Comparator + VDD Control and Driver Logic LX GND Oscillator and Shutdown Control EN Slope Compensation Current Sense PGND LDRI LFB VREF = 0.2V DS9278-04 August 2007 + www.richtek.com 5 RT9278 Preliminary 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. www.richtek.com 6 DS9278-04 August 2007 RT9278 Preliminary Absolute Maximum Ratings l l l l l l l l l (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 4) VDFN-10L 3x3, θJA --------------------------------------------------------------------------------------------------- 70°C/W Lead Temperature (Soldering, 10 sec.)-------------------------------------------------------------------------- 260°C Operation Temperature Range ------------------------------------------------------------------------------------ −40°C to 85°C Storage Temperature Range --------------------------------------------------------------------------------------- − 65°C to 150°C ESD Susceptibility (Note 2) HBM (Human Body Mode) ----------------------------------------------------------------------------------------- 2kV Recommended Operating Conditions l l (Note 3) Ambient Temperature Range -------------------------------------------------------------------------------------- 0°C to 70°C Junction Temperature Range -------------------------------------------------------------------------------------- 0°C to 125°C Electrical Characteristics (VBAT = 1.8V, VOUT = 3.3V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Units -- 1.5 -- V Start-Up Voltage VST Operating Voltage Range, After start-up VBAT 1.1 -- 5.5 V VOUT Output Voltage Range VOUT_ADJ 2.4 -- 5.5 V -- 6.5 -- V IL = 1mA VOUT Over Voltage Protection Switch-off Current I (VBAT) ISW OFF VOUT = 3.3V, VFB = 0.9V -- 200 350 µA Shutdown Current IOFF EN Pin = 0V, Open Loop -- 0.01 1 µA Feedback Reference Voltage VFB Close Loop, V OUT = 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 -- uA Compensation Sink Current -- 22 -- uA Current Limit Setting ISW Error Amplifier To be continued DS9278-04 August 2007 www.richtek.com 7 RT9278 Parameter Preliminary Symbol Test Conditions Min Typ Max Units -- 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 TSD -- 180 -- °C Thermal Shutdown Hysterises ∆TSD -- 20 -- °C 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. θJA is measured in the natural convection at T A = 25°C on a high effective thermal conductivity test board of JEDEC 51-7 (2S2P, 4-Layers) thermal measurement standard. www.richtek.com 8 DS9278-04 August 2007 RT9278 Preliminary Typical Operating Characteristics Reference Voltage vs. Temperature Frequency vs. Temperature 0.804 700 0.803 Reference Voltage (V) 660 640 620 600 0.802 0.801 0.8 0.799 0.798 0.797 VDD = 3.3V VDD = 3.3V 0.796 580 -40 -20 0 20 40 60 -40 -20 80 100 120 140 160 180 0 Efficiency vs. Output Current 80 100 120 140 160 180 60 = = = = 3.0V 2.5V 2.0V 1.5V 50 40 30 20 10 VOUT = 5.0V 90 80 Efficiency (%) VIN VIN VIN VIN 70 100 Refer to Application Circuit Figure 3 VOUT = 3.3V 80 Efficiency (%) 60 Efficiency vs. Output Current 90 VIN VIN VIN VIN VIN VIN VIN 70 60 50 40 30 = = = = = = = 4.5V 4.0V 3.5V 3.0V 2.5V 2.0V 1.5V 20 10 0 0 1 10 100 1000 1 10 Output Current (mA) 100 1000 Output Current (mA) Input Voltage vs. Output Voltage Input Voltage vs. Output Voltage 3.350 5.150 3.325 5.100 Output Voltage (V) Output Voltage (V) 40 Temperature (°C) Temperature (°C) 100 20 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 VOUT = 3.3V VOUT = 5.0V 3.200 4.850 1.6 1.8 2.0 2.2 2.4 Input Voltage (V) DS9278-04 August 2007 2.6 2.8 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) www.richtek.com 9 RT9278 Preliminary Output Voltage vs. Output Current 4.98 3.305 3.300 4.97 4.96 3.295 4.95 Output Voltage (V) Output Voltage (V) Output Voltage vs. Output Current 3.310 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 3.250 1 10 100 4.91 4.90 4.89 4.88 4.87 4.86 4.85 VIN VIN VIN VIN VIN VIN VIN VOUT = 5.0V 1 10 = = = = = = = 4.2V 4.0V 3.5V 3.0V 2.5V 2.0V 1.5V 100 Output Current (mA) Power LED Efficiency vs. Input Voltage Normal Operation 80 70 60 50 40 30 20 Vf = 3.5V, ILED = 200mA, L = 4.7µH Refer to Application Circuit Figure 1 Output Current (mA) 90 Power LED Efficiency (%) 4.92 1000 100 10 4.94 4.93 1000 VOUT (10mV/Div) (5V/Div) VLX (1V/Div) VIN II N (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 II N (1A/Div) II N VIN = 1.5V, VOUT = 5V, ILOAD = 300mA Time (1µs/Div) www.richtek.com 10 (5V/Div) (500mA/Div) VIN = 4.2V, VOUT = 5V, ILOAD = 100mA Time (1µs/Div) DS9278-04 August 2007 RT9278 Preliminary Normal Operation VIN = 1.5V, VOUT = 5V, ILOAD = 100mA to 300mA (1V/Div) VLX (5V/Div) II N (500mA/Div) VIN = 4.2V, VOUT = 5V, ILOAD = 300mA Output Voltage Deviation (mV) Load Current (mA) (10mV/Div) VOUT VIN Load Transient Regulation 400 200 0 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 ILED -100 II N (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) ILED ILED II N (500mA/Div) Mode Transition Time (10ms/Div) DS9278-04 August 2007 II N (500mA/Div) Time (10ms/Div) www.richtek.com 11 RT9278 Preliminary 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. Output Capacitor Selection For lower output voltage ripple, low-ESR ceramic capacitors are recommended. The tantalum capacitors can be used 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 × ESRCOUT + IPP 2× C× f Output Voltage Setting Referring to application circuits (Figure 6), the output voltage of the switching regulator (VOUT ) can be set with below equation : R2 VOUT = (1 + ) × VFB, 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 (W) The criterion for selection of package is the junction temperature below the maximum desired temperature with the maximum expected ambient temperature. Layout Guide Input Capacitor Selection 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. www.richtek.com 12 l l l 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. l Minimized FB node copper area and keep far away from noise sources. l The MOSFETs of linear regulator should have wide pad to dissipate the heat. DS9278-04 August 2007 RT9278 Preliminary Outline Dimension D2 D L E E2 SEE DETAIL A 1 e 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. Symbol Dimensions In Millimeters Dimensions In Inches 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 Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)89191466 Fax: (8862)89191465 Email: [email protected] DS9278-04 August 2007 www.richtek.com 13