SP7648

Solved by SP7648 TM Low Reference High efficiency Boost Regulator FeaTUReS ■ True Shutdown ■ 700mA Output Current at 3.3V Input; 4.2V output ■ 92% Efficiency from 2.7V IN to 3.3VOUT ■ Wide Input Voltage Range: 2.7V to 4.5V ■ 5V Fixed or Adjustable Output ■ 0.3 Switch ■ Integrated Synchronous Rectifier:0.3 ■ Anti-Ringing Switch Technology ■ Programmable Inductor Peak Current ■ Logic Shutdown Control ■ Low 0.8V or 0.288V Reference Voltage ■ Small 10 pin DFN or MSOP Package V BATT  2 3 4 5 0 V OUT FLASH NC (Test) R LIM SP7648 10 Pin DFN 9 LX 8P GND 7 GND 6 FB SHDN Now Available in Lead Free Packaging aPPLicaTiOnS ■ LED Driver ■ Camera Flash ■ Handheld Portable Devices DeScRiPTiOn The SP7648 is an ultra-low quiescent current, high efficiency step-up DC-DC converter ideal for single cell Li-Ion or dual cell alkaline battery applications to drive various LEDs. The SP7648 combines low quiescent current and excellent light-load efficiency of PFM control. The SP7648 features synchronous rectification, a 0.3 charging switch, an anti-ringing inductor switch, undervoltage lockout and programmable inductor peak current. The device can be shut down by a 1nA active LOW shutdown pin. A very low 0.288V reference voltage is optimized for driving a constant current load. TYPicaL aPPLicaTiOn ciRcUiT 4.7µH Vin (2.7 - 4.5V) 0µF VBATT On/OFF SHDN RLIM RLIM 1.0K ® SP7648 LX 0µF 0.33 D VOUT NC 470pF FLASH GND PGND FB 1K R2 Q R FLaSH Mar16-06 Rev B SP7648 Ultra-low Quiescent Current, High Efficiency Boost Regulator © 2006 Sipex Corporation  aBSOLUTe MaXiMUM RaTingS LX, Vo, VBATT, FLASHOUT, FB to GND pin ...................... -0.3 to 6.0V SHDN, FLASH ..................................................... -0.3V to VBATT+1.0V Vo, GND, LX Current ....................................................................... 2A Reverse VBATTCurrent .............................................................. 220mA Forward VBATTCurrent .............................................................. 500mA Storage Temperature .................................................. -65 °C to 150°C Operating Temperature ................................................ -40°C to +85°C ESD Rating ........................................................................ 1.5kV HBM These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. eLecTRicaL SPeciFicaTiOnS VBATT =VSHDN = 3.6V, VFB=ZeroV, ILOAD = 0mA, TAMB= -40°C to +85°C, VOUT = 5.0V, typical values at 27°C unless otherwise noted. The denotes the specifications which apply over full operating temperature range -40ºC to +85°C, unless otherwise specified. PaRaMeTeR Input Voltage Operating Range, VBATT Output Voltage Range, VOUT Under Voltage Lock-out/UVLO Output Voltage, VO Shutdown Current into VO, ISDO Shutdown Current into VBATT, ISDB Efficiency Inductor Peak Current Limit, IPK Output Current (Note 2) Minimum Off-Time Constant KOFF Maximum On-Time Constant KON Enable Valid to Output Stable (Note 3) NMOS Switch Resistance PMOS Switch Resistance FB Set Voltage, VFB FB Input Current SHDN Input Voltage (Note 1) VIL VIH SHDN Input Current LX Pin Leakage FLASH Threshold V IL VIH 650 0.5 2.0 0.76 0.266 2.0 1.0 Min 2.7 2.7 0.5 4.6 TYP 0.61 5.0  250 92 800 600 800 400 200 1.0 3.5 300 0.30 0.30 0.8 0.288   MaX 4.5 5.5 0.7 5.4 500 750 000 1.5 5.0 500 0.6 0.6 0.84 0.310 00 0.5 00 3 0.4 V V nA V nA µA V V UniTS V V V V nA nA % mA mA mA mA mA V*µs V*µs µs Internal Feedback Divider VSHDN = ZeroV VSHDN = ZeroV, VBATT = 2.7V VBATT = 2.7V, IOUT = 200mA, RLIM = 2k RLIM = 2k , IPK = 1600/RLIM RLIM = 1k , IPK = 1600/RLIM VBATT = 2.7V, RLIM =1k VBATT = 2.7V, RLIM =2k VBATT = 2.7V, RLIM = 4k KOFF T OFF (VOUT - VBATT) KON T ON (VBATT) ILOAD = mA INMOS = 00mA IPMOS = 00mA External feedback Flash = 0 External feedback Flash = 1 VFB =1.3V VBATT = 2.7V VBATT = 2.7V cOnDiTiOnS After Startup note 1:SHDN must transition faster than 1V/100mS for proper operation. note 2:Output Current I = VIN { VOUT } X Efficiency x {Inductor Peak Current - Inductor Ripple Current} 2 note 3:Guaranteed by Design. Mar16-06 Rev B SP7648 Ultra-low Quiescent Current, High Efficiency Boost Regulator © 2006 Sipex Corporation 2 Pin DeScRiPTiOn Pin nUMBeR 1 Pin naMe VBATT DeScRiPTiOn Battery Voltage. The startup circuitry is powered by this pin. Battery Voltage is used to calculate switch off time: TOFF= K OFF/ (VOUTVBATT). When the battery voltage drops below 0.61V the SP7648 goes into an undervoltage lockout mode (UVLO), where the part is shut down. 2 3 4 FLASH NC (Test) RLIM Reference Control Input. Internal Reference defaults to 0.8V if FLASH = LOW and 0.288V if FLASH = HIGH. No connection. This pin is bonded out for test purposes only and must be left floating in all applications. Current Limit Resistor. By connecting a resistor RLIM from this pin to ground the inductor peak current is set by IPEAK=1600/RLIM. The range for RLIM is 9k (for 180mA) to 1.K (for 1.6A). 5 6 SHDN FB Shutdown Not. Tie this pin high to V BATT,for normal operation. Pull this pin to ground to disable all circuitry inside the chip. Feedback. Connect this pin to GND for fixed +5V operation. Connect this pin to a resistor voltage divider between VOUTand GND for adjustable output operation. 7 8 9 GND PGND LX Ground. Connect to ground plane. Power Ground. The inductor charging current flows out of this pin. Inductor Switching Node. Connect one terminal of the inductor to the positive terminal of the battery. Connect the second terminal of the inductor to this pin. The inductor charging current flows into LX, through the internal charging N-channel FET, and out the PGND pin. 10 VOUT Output Voltage. The inductor current flows out of this pin during switch off-time. It is also used as the internal regulator voltage supply. Connect this pin to the positive terminal of the output capacitor. Note that the Thermal Pad (Pin 11) should be connected to Ground. Mar16-06 Rev B SP7648 Ultra-low Quiescent Current, High Efficiency Boost Regulator © 2006 Sipex Corporation 3 FUncTiOnaL DiagRaM @ @ @ @ @ @ @ @ @ @ @ @@ @ @ @ @ @ Mar16-06 Rev B SP7648 Ultra-low Quiescent Current, High Efficiency Boost Regulator © 2006 Sipex Corporation 4 THeORY OF OPeRaTiOn Detailed Description The SP7648 is a step-up DC-DC converter with an input voltage operation range from 2.7V to 4.7V. In addition to the main 0.3 internal NMOSFET switch the SP7648 has an internal synchronous rectifier, thereby increasing efficiency and reducing the space and cost of an external diode. An internal inductive-damping switch significantly reduces inductive ringing for low noise-high efficiency operation. If the supply voltage drops below 0.61V the SP7648 goes into under voltage lockout, thus opening both internal switches. The inductor peak current is externally programmable to allow for a range of inductor values. devices, the inductor and input & output filter capacitors should be soldered with their ground pins as close together as possible in a star-ground configuration. The VOUT pin must be bypassed directly to ground as close to the SP7648 devices as possible (within 0.2in or 5mm). The DC-DC converter and any digital circuitry should be placed on the opposite corner of the PC board as far away from sensitive RF and analog input stages. Noisy traces, such as from the LX pin, should be kept away from the voltagefeedback VFB node and separated from it using grounded copper to minimize EMI. S ee the SP7648EB Evaluation Board Manual for PC Board Layout design details. Circuit Layout Printed circuit board layout is a critical part of a power supply design. Poor designs can result in excessive EMI on the feedback paths and on the ground planes with applications involving high switching frequencies and large peak currents. Excessive EMI can result in instability or regulation errors. All power components should be placed on the PC board as closely as possible with the traces kept short, direct, and wide (>50mils or 1.25mm). Extra copper on the PC board should be integrated into ground as a pseudoground plane. On a multilayer PC board, route the star ground using componentside copper fill, then connect it to the internal ground plane using vias. For the SP7648 Control Scheme A minimum off-time, current limited pulse frequency modulation (PFM) control scheme combines the high output power and efficiency of a pulse width modulation (PWM) device with the ultra low quiescent current of the traditional PFM. At low to moderate output loads the PFM control provides higher efficiency than traditional PWM converters are capable of delivering. At these loads the switching frequency is determined by a minimum off-time (TOFF, MIN) and a maximum on-time (TON, MAX) where: TOFF < KOFF / (VOUT - VBATT) TON > KON / VBATT KOFF = 1.0Vµs KON = 3.5 Vµs Mar16-06 Rev B SP7648 Ultra-low Quiescent Current, High Efficiency Boost Regulator © 2006 Sipex Corporation 5 THeORY OF OPeRaTiOn At light loads (as shown in plot A in Figure 1) the charge cycle will last the maximum value for tON: For a 3V battery this would be as follows: TON= K ON/ V BATT= 3.5V µS/ 3V = 1.17µS. The current built up in the coil during the charge cycle gets fully discharged in the discontinuous conduction mode (DCM). When the current in the coil has reached zero, the synchronous rectifier switch is opened and the voltage across the coil (from VBATTto LX) is shorted internally to eliminate inductive ringing. With increasing load (as shown in plot B in Figure 1) this inductor damping time becomes shorter, because the output will quickly drop below its regulation point due to heavier load. If the load current increases further, the SP7648 enters continuous conduction mode (CCM) where there is always current flowing in the inductor. The charge time remains at maximum TONas long as the inductor peak current limit is not reached as shown in plot C in Figure 1. The inductor peak current limit can be programmed by tying a resistor RLIM from the RLIM pin to ground where: IPEAK = 1600 / RLIM When the peak current limit is reached the charge time is short-cycled. In plot D of Figure 1, the switch current reaches the peak current limit during the charge period which ends the charge cycle and starts the discharge cycle. However, full load is not yet achieved because at the end of the minimum discharge time the output was still within regulation. Maximum load is reached when this discharge time has shrunk to the minimum allowed value TOFFas shown in Plot E of Figure 1. Component Selection inductor current vs. Load llim Ton Max. Toff Min. E. Iripple=Toff* (Vo - Vi)/L llim Ton Max. Toff Min. D. Toff*= (Vo - Vi)/L