RT9278. High Efficiency Boost LDO Converter & High Power White LED Driver. General Description. Features. Applications. Ordering Information

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1 RT High Efficiency Boost LDO Converter & High Power White LED Driver General Description The RT 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 RT is boost converter with PWM control loop, provide up to % efficiency by using a synchronous rectifier. The maximum peak current in the internal switch is limited to up to A. 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. RT is available in VDFN-L 3x3 package. Ordering Information RT Note : Richtek products are : Package Type QV : VDFN-L 3x3 (V-Type) Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-. Suitable for use in SnPb or Pb-free soldering processes. Features % Efficiency Synchronous Boost Converter High Supply Capability A Current Limit Input Voltage Range :.V to.v 6kHz Fixed Switching Rate Adjustable Output Voltage Options Up to.v Output Voltage Keep Regulated when Input Voltage Exceed Setting Output Voltage ua Supply Current in Shutdown Mode External Compensation Network Build in Linear Controller for Linear Regulator Over Temperature Protection Small -Lead VDFN Package RoHS Compliant and % Lead (Pb)-Free Applications Digital Still Camera Camera White LED Flash Light PDAs Portable Device Marking Information RTPQV AC-YM DNN AC- : Product Code YMDNN : Date Code Pin Configurations (TOP VIEW) RTQQV AC=YM DNN AC= : Product Code YMDNN : Date Code COMP 3 EN LDRI VDD VDFN-L 3x3

2 Typical Application Circuit L to µh C.µF Chip Shutdown C nf Chip Enable R ms.k 3 EN VDD RT 6 COMP LDRI C3 µf C.µF Q AO 3k ms D Power LED R3. ma Note : Patent Pending. Figure. Novel Up-Down Driver for Power LED with Strobe Mode Chip Enable EN VDD L to µh Chip Shutdown RT C 6.µF R.k COMP LDRI 3 C nf R = kω Figure. Novel Up-Down Driver for Power LED with Strobe Mode and Movie Mode Note : Patent Pending. The Signal has to pull high before enable IC. C3 µf R.k C.µF R k Q AO33 3k I strobe ma I Movie ma ms D Power LED R3..V V. R3 = IStrobe (_HI.) x R R =. (IMovie x R3) Chip Enable L.uH C µf Chip Shutdown R.k C.nF EN VDD RT 6 COMP LDRI 3 C3 µf C µf k Q AO33 C pf R3 k V OUT 3.3V R k Figure 3. Synchronous Boost Converter with Load Disconnect in Shutdown

3 .6V to V L.µH C µf R k C 3.3nF 3 EN VDD RT 6 COMP LDRI C3 µf C pf 3k R3 6k C µf Q AO33 R k R 6k R6.k C6 pf C µf V OUT 3.3V Figure. Boost-LDO Application for Constant Output Voltage.6V to 3.V L.µH C µf R 3.k C.nF 3 EN VDD RT 6 COMP LDRI C3 µf C pf k R3 k V OUT 3.3V/3mA C µf Q AO33 R k R k R6 k C6 pf V OUT.V/mA C 3µF Figure. Synchronous Boost Converter Driver for Dual Output Voltage Chip Enable C µf L Chip Shutdown R COMP C COMP EN VDD RT LDRI PVD COMP 3 C3 µf C FF R C OUT µf V OUT Figure 6. Synchronous Boost Converter 3

4 Table. Component Selection for Figure 6 (L=.mH) Input Voltage Output Voltage L (mh) C OUT (mf) R R COMP C COMP (nf) C FF (pf).~ ~ ~ Table. Component Selection for Figure 6 (L=.mH) Input Voltage Output Voltage L (mh) C OUT (mf) R R COMP C COMP (nf) C FF (pf).~ ~ ~ Table 3. Component Selection for Figure 6 (L=6.mH) Input Voltage Output Voltage L (mh) C OUT (mf) R R COMP C COMP (nf) C FF (pf).~ ~ ~ Table. Component Selection for Figure 6 (L=mH) Input Voltage Output Voltage L (mh) C OUT (mf) R R COMP C COMP (nf) C FF (pf).~ ~ ~.. 3 6

5 Functional Pin Description Pin No. Pin Name Pin Function Feedback Input Pin. COMP Feedback Compensation Pin. 3 Ground. EN Enable Input Pin Switch Node. 6 Output Pin VDD Device Input Power Pin. Power Ground. LDRI Linear Controller Driver Output. Linear Controller Feedback Input. (Exposed Pad) The exposed pad must be soldered to a large PCB and connected to for maximum power dissipation. RT Function Block Diagram COMP VDD V REF =.V Error AMPLIFIER - + Error Comparator - + Control and Driver Logic EN Oscillator and Shutdown Control Slope Compensation Current Sense LDRI V REF =.V - +

6 Operation RT 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 ua 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 ua. The soft-start time is set by the following formula : R COMP and C COMP are compensation components. T SS (V - μa x R = μa COMP ) x C COMP 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.V, 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 C, the controllers are shutdown. 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. 6

7 Absolute Maximum Ratings (Note ) Supply Voltage, V DD V Pin Voltage V to V The Other pins V to V Power Dissipation, P T A = C VDFN-L 3x W Package Thermal Resistance (Note ) VDFN-L 3x3, θ JA C/W Lead Temperature (Soldering, sec.) C Junction Temperature C Storage Temperature Range C to C ESD Susceptibility (Note 3) HBM (Human Body Mode) kv Recommended Operating Conditions (Note ) Ambient Temperature Range C to C Junction Temperature Range C to C Electrical Characteristics (V BAT =.V, V OUT = 3.3V, T A = C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Start-Up Voltage V ST I L = ma V Operating Voltage Range, After start-up V BAT. --. V Output Voltage Range V OUT_ADJ. --. V Over Voltage Protection V Switch-off Current I (V BAT ) I SW OFF V OUT = 3.3V, V =.V -- 3 μa Shutdown Current I OFF EN Pin = V, Open Loop --. μa Feedback Reference Voltage V Close Loop, V OUT = 3.3V...6 V Switching Frequency f S khz Maximum Duty D (MAX) % SWN Switch ON Resistance V OUT = 3.3V mω SWP Switch ON Resistance V OUT = 3.3V mω Current Limit Setting I SW V OUT = 3.3V A Error Amplifier GM ms Compensation Source Current μa Compensation Sink Current μa

8 Linear Controller Parameter Symbol Test Conditions Min Typ Max Unit Feedback Voltage for Linear Controller V V EN Input High Level Threshold V EN Input Low Level Threshold V Thermal Shutdown T SD C Thermal Shutdown Hysteresis ΔT SD C Note. 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. θ JA is measured at T A = C on a high effective thermal conductivity four-layer test board per JEDEC -. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note. The device is not guaranteed to function outside its operating conditions.

9 Typical Operating Characteristics Frequency vs. Temperature Reference Voltage vs. Temperature VDD = 3.3V. VDD = 3.3V 6.3 Frequency (khz) Reference Voltage Temperature ( C) Temperature ( C) Efficiency vs. Output Current Efficiency vs. Output Current Efficiency (%) 6 3 = 3.3V VIN = 3.V VIN =.V VIN =.V VIN =.V Refer to Application Circuit Figure 3 Efficiency (%) 6 3 = V VIN =.V VIN =.V VIN = 3.V VIN = 3.V VIN =.V VIN =.V VIN =.V Refer to Application Circuit Figure 3 Output Current (ma) Output Current (ma) Input Voltage vs. Output Voltage Input Voltage vs. Output Voltage 3.3 = 3.3V. = V 3.3. Output Voltage Output Voltage Input Voltage Input Voltage

10 Output Voltage vs. Output Current Output Voltage vs. Output Current 3.3. Output Voltage = 3.3V VIN = 3.V VIN =.V VIN =.V VIN =.V Output Voltage = V VIN =.V VIN =.V VIN = 3.V VIN = 3.V VIN =.V VIN =.V VIN =.V Output Current (ma) Output Current (ma) Power LED Efficiency vs. Input Voltage Normal Operation Power LED Efficiency (%) 6 3 Vf = 3.V, ILED = ma, L =.μh Refer to Application Circuit Figure V OUT V (mv/div) (V/Div) (V/Div) VIN =.V, = V, ILOAD = ma Time (μs/div) Input Voltage Normal Operation Normal Operation V OUT V OUT (mv/div) (mv/div) (V/Div) VIN (V/Div) V (V/Div) V (V/Div) (A/Div) VIN =.V, = V, ILOAD = 3mA VIN =.V, = V, ILOAD = ma Time (μs/div) Time (μs/div)

11 Normal Operation Load Transient Regulation (mv/div) VIN =.V, = V, ILOAD = ma to 3mA VIN (V/Div) Load Current (ma) V (V/Div) VIN =.V, = V, ILOAD = 3mA Output Voltage Deviation (mv) - Time (μs/div) Time (ms/div) Load Current (ma) Output Voltage Deviation (mv) - Load Transient Regulation VIN =.V, = V, ILOAD = ma to ma VIN I LED Flash LED VIN = 3.V, Power LED = ma to ma (V/Div) (ma /Div) (mv/div) Time (ms/div) Time (ms/div) Flash LED VIN = 3.V, Power LED = ma to ma (mv/div) (V/Div) Flash LED VIN =.3V, Power LED = ma to ma (mv/div) (V/Div) (ma /Div) ILED I LED Mode Transition Time (ms/div) Time (ms/div)

12 Application Information RT 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 % to % of the maximum input current. If the selection is % I PK = I IN(MAX) (I =. I L = η. I + I OUT(MAX) η V IN(MIN) RIPPLE V IN(MIN) [V OUT(MAX) OUT OUT V =. I - V OUT IN(MIN) f IN(MAX) The minimum inductance value is derived from the following equation : ] OSC Depending on the application, the recommended inductor value is between.μh and μh. Input Capacitor Selection For better input bypassing, low-esr ceramic capacitors are recommended for performance. A μf input capacitor is sufficient for most applications. For a lower output power requirement application, this value can be decreased. 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. V = V I RIPPLE PEAK ESRC RIPPLE(ESR) OUT below equation : = (+ ) V R V =.V (typ.) + V IPP + C f RIPPLE(C) Output Voltage Setting Referring to application circuits (Figure 6), the output voltage of the switching regulator (V OUT ) can be set with Linear Regulator Linear Regular MOSFETs Selection The linear controller of RT 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 = ( V OUT ) x I OUT (W) The criterion for selection of package is the junction temperature below the maximum desired temperature with the maximum expected ambient temperature. Layout Consideration A full plane without gap break. V DD to noise bypass Short and wide connection for the μf MLCC capacitor between Pin and Pin3. to noise bypass Add a capacitor close to L inductor, when is not an ideal voltage source., Minimized node copper area and keep far away from noise sources. The MOSFETs of linear regulator should have wide pad to dissipate the heat.

13 Outline Dimension D D L E E SEE DETAIL A e b A A A3 DETAIL A Pin # ID and Tie Bar Mark Options Note : The configuration of the Pin # identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A A.... A3.... b..3.. D D E E....6 e.. L.3... V-Type L DFN 3x3 Package Richtek Technology Corporation F, No., Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (63)6 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. 3