SP7648ER-L/TR

SP7648 Low Reference High Efficiency Boost Regulator November 2012 Rev. 2.0.0 GENERAL DESCRIPTION APPLICATIONS 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 0.3Ω charging switch, an anti-ringing inductor switch, under-voltage 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.  LED Driver  Camera Flash  Handheld Portable Devices FEATURES  True Shutdown  700mA Output Current at 3.3V Input; 4.2V output  92% Efficiency from 2.7VIN to 3.3VOUT  2.7V to 4.5V Wide Input Voltage Range  5V Fixed or Adjustable Output  0.3Ω Switch  Integrated Synchronous Rectifier:0.3Ω  Anti-Ringing Switch Technology  Programmable Inductor Peak Current  Logic Shutdown Control  Low 0.8V or 0.288V Reference Voltage  Small 10-pin DFN and MSOP Package TYPICAL APPLICATION DIAGRAM Fig. 1: SP7648 Application Diagram Exar Corporation 48720 Kato Road, Fremont CA 94538, USA www.exar.com Tel. +1 510 668-7000 – Fax. +1 510 668-7001 SP7648 Low Reference High Efficiency Boost Regulator ABSOLUTE MAXIMUM RATINGS OPERATING RATINGS 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. Input Voltage Range VBATT............................ 2.7V to 4.5V Ambient Temperature Range ................... -40°C to +85°C Thermal Resistance ...................................................... θJA (DFN-10) ............................................... 40.5°C/W θJA (MSOP-10) .......................................... 214.0°C/W 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 VBATT Current .......................................... 220mA Forward VBATT Current.......................................... 500mA Storage Temperature .............................. -65°C to 150°C ESD Rating (HBM - Human Body Model) .................. 1.5kV ELECTRICAL SPECIFICATIONS Specifications with standard type are for an Operating Ambient Temperature of TA = 27°C only; limits applying over the full Operating Ambient Temperature range are denoted by a “•”. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at T A = 27°C, and are provided for reference purposes only. Unless otherwise indicated, V BATT = VSHDN = 3.6V, VFB = ZeroV, ILOAD = 0mA, VOUT = 5.0V, TA= –40°C to 85°C. Parameter Min. Typ. Max. Units Conditions Input Voltage Operating Range VBATT 2.7 - 4.5 V • Output Voltage Range V OUT 27 - 5.5 V • Under Voltage Lock-out UVLO 0.5 0.61 0.7 V • Output Voltage VO After Startup 4.6 5.0 5.4 V • Internal Feedback Divider Shutdown Current into VO, ISDO - 1 500 nA • VSHDN = ZeroV Shutdown Current into VBATT, ISDB - 250 750 nA • VSHDN = ZeroV, VBATT = 2.7V 92 - % 800 1000 Efficiency Inductor Peak Current Limit, IPK 650 1600 VBATT = 2.7V, IOUT = 200mA, RLIM= 2kΩ mA • mA • 800 Output Current (Note 2) RLIM = 2kΩ, IPK = 1600/RLIM RLIM = 1kΩ, IPK = 1600/RLIM VBATT = 2.7V, RLIM =1kΩ 400 200 VBATT = 2.7V, RLIM =2kΩ VBATT = 2.7V, RLIM = 4kΩ Minimum Off-Time Constant KOFF 0.5 1.0 1.5 V*µs • KOFF ≤TOFF (VOUT - VBATT) Maximum On-Time Constant KON 2.0 3.5 5.0 V*µs • KON ≥TON (VBATT) Enable Valid to Output Stable (Note 3) 300 500 µs NMOS Switch Resistance 0.30 0.6 Ω • INMOS = 100mA PMOS Switch Resistance 0.30 0.6 Ω • IPMOS = 100mA 0.76 0.8 0.84 0.266 0.288 0.310 V • - 1 100 nA • VFB =1.3V 0.5 V • VBATT = 2.7V 100 nA 3 µA FB Set Voltage, VFB FB Input Current SHDN Input Voltage VIL (Note 1) SHDN Input Voltage VIH (Note 1) 2.0 SHDN Input Current 1 LX Pin Leakage FLASH Threshold V 0.4 IL FLASH Threshold VIH 1.0 ILOAD = 1mA External feedback Flash = 0 External feedback Flash = 1 • V 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 © 2012 Exar Corporation 2/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator Note 3: Guaranteed by Design. BLOCK DIAGRAM Fig. 2: SP7648 Block Diagram PIN ASSIGNMENT Fig. 3: SP7648 Pin Assignment © 2012 Exar Corporation 3/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator PIN DESCRIPTION Name Pin Number VBATT 1 Battery Voltage. The startup circuitry is powered by this pin. Battery Voltage is used to calculate switch off time: TOFF= KOFF/ (VOUT-VBATT). When the battery voltage drops below 0.61V the SP7648goes into an undervoltage lockout mode (UVLO), where the part is shutdown. FLASH 2 Reference Control Input. Internal Reference defaults to 0.8V if FLASH= LOW and 0.288V if FLASH = HIGH. NC (Test) 3 No connection. This pin is bonded out for test purposes only and must be left floating in all applications. RLIM 4 Current Limit Resistor. By connecting a resistor RLIM from this pin t ground the inductor peak current is set by IPEAK=1600/RLIM. The range for RLIM is 9kΩ (for 180mA) to 1KΩ (for 1.6A). SHDN 5 Shutdown Not. Tie this pin high to VBATT, for normal operation. Pull this pin to ground to disable all circuitry inside the chip. FB 6 Feedback. Connect this pin to GND for fixed +5V operation. Connect this pin to a resistor voltage divider between VOUT and GND for adjustable output operation. GND 7 Ground. Connect to ground plane. PGND 8 Power Ground. The inductor charging current flows out of this pin. 9 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. VOUT 10 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. GND Thermal Pad LX Description Connect to ground signal. ORDERING INFORMATION Part Number SP7648ER-L SP7648ER-L/TR SP7648EU-L SP7648EU-L/TR Ambient Temperature Range -40°C≤TA≤+85°C -40°C≤TA≤+85°C Marking SP76 48ER WWX 7648 EXXX YWW Packing Quantity Package DFN-10 MSOP-10 Note 1 Note 2 Bulk 3K/Tape & Reel Bulk 2.5K/Tape & Reel “YY” = Year – “WW” = Work Week – “X” = Lot Number; when applicable. © 2012 Exar Corporation 4/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator TYPICAL PERFORMANCE CHARACTERISTICS Fig. 4: Output Current versus Input Voltage Fig. 5: Efficiency versus Input Voltage Fig. 6: Output Current versus Input Voltage Fig. 7: Efficiency versus Input Voltage Fig. 8: Output Current versus Input Voltage Fig. 9: Efficiency versus Input Voltage © 2012 Exar Corporation 5/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator Fig. 10: Startup 200mA Torch VIN= 3.6V, VOUT=3.9V, CH1=SHDN(5V/div), CH2=VOUT(1V/div), CH3=Iin(1A/div) Fig. 11: Startup 700mA Flash VIN= 3.6V, VOUT=3.65V, CH1=SHDN(5V/div), CH2=VOUT(1V/div), CH3=Iin(1A/div) Fig. 12: Ripple 200mA Torch VIN= 3.6V, VOUT=3.9V, CH1=VIN(AC 100mV/div), CH2=VOUT(AC 100mV/div) Fig. 13: Ripple 700mA Flash VIN= 3.6V, VOUT=3.65V, CH1=VIN(AC 100mV/div), CH2=VOUT(AC 100mV/div) © 2012 Exar Corporation 6/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator THEORY OF OPERATION 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: 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 0.3Ω 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 inductivedamping 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. TOFF ≤ KOFF/ (VOUT- VBATT) TON ≥ KON/ VBATT KOFF= 1.0Vμs CIRCUIT LAYOUT KON = 3.5 Vμs 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 pseudo-ground plane. On a multilayer PC board, route the star ground using component-side copper fill, then connect it to the internal ground plane using vias. For the SP7648 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 voltage-feedback VFB node and separated from it using grounded copper to minimize EMI. See the SP7648EB Evaluation Board Manual for PC Board Layout design details. At light loads (as shown in plot A in Figure 14) the charge cycle will last the maximum value for tON: For a 3V battery this would be as follows: TON= KON/ VBATT= 3.5VμS/ 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 VBATT to LX) is shorted internally to eliminate inductive ringing. With increasing load (as shown in plot B in Figure 14) 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 TON as long as the inductor peak current limit is not reached as shown in plot C in Figure 14. The inductor peak current limit can be programmed by tying a resistor RLIM from the RLIM pin to ground where: © 2012 Exar Corporation IPEAK= 1600 / RLIM When the peak current limit is reached the charge time is short-cycled. In plot D of Figure 14, the switch current reaches the peak current limit during the charge period which ends the charge cycle and starts the discharge 7/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator COMPONENT SELECTION 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 TOFF as shown in Plot E of Figure 14. Selection of capacitors for SP7648 power supply circuits can be made through the use of the Component Selection Table. Capacitor equivalent series resistance (ESR) in the range of 0.2 to 0.3Ω is a requirement for obtaining sufficient output voltage ripple for the SP7648 to properly regulate under its load. For example, in the SP7648 application circuit a 10μF, 10V, X5R, surface mount ceramic output filter capacitor is used. Ceramic capacitors have an ESR too low to produce enough output ripple for the SP7648 to regulate the output; therefore, a 0.33Ω resistor is added in series with the 10μF capacitor at the VOUT pin. Designers should select input and output capacitors with a rating exceeding the inductor current ripple, which is typically set by the inductor value and the KON value as given in the following relationship: I L(RIPPLE) = KON/L, where KON = 3.5V*μS Fig. 14: Inductor Current versus Load Table 1: Component Selection © 2012 Exar Corporation 8/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator For the example, a 10μH inductor would have an inductor current ripple of 350mA, while a 4.7μH inductor would have an inductor current ripple value of 740mA. Do not allow tantalum capacitors to exceed their ripple-current ratings. An input filter capacitor can reduce peak currents drawn from the battery and improve efficiency. For most applications, use the same capacitor for the input and output. Low-ESR tantalum capacitors are acceptable provided they meet the ESR requirement of 0.2Ω to 0.3Ω. In selecting an inductor, the saturation current specified for the inductor needs to be greater than the SP7648 peak current to avoid saturating the inductor, which would result in a loss of efficiency and could damage the inductor. The SP7648 evaluation board uses a Wurth 4.7μH inductor with an ISAT value of 1.7A and a DCR of 0.065Ω, which handles the IPEAK of 1.6A of the SP7648 and will deliver high efficiencies. Other inductors could be selected provided their ISAT is greater than the IPEAK of the SP7648. values could be selected using the above relationships. USING THE FLASH CONTROL PIN The SP7648 will regulate the output by the equations above depending on the state of the FLASH pin. When the FLASH pin is low (0.4V), the internal reference voltage is defined as 0.288V. This allows the use of smaller values for the sense resistor for current regulation mode. This improves efficiency and reduces the physical size of the sense resistor. An external MOSFET switch can be used to change the sense resistor when changing to the Flash Mode. HIGH BRIGHTNESS WHITE LED For the high brightness LumiLED white LED application, the SP7648 is generally programmed as a current source. The bias resistors R1 and R2 are used to set the operating current of the white LED with the equation: VOUT PROGRAMMING The SP7648 can be programmed as either a voltage source or a current source. To program the SP7648 as voltage source, the SP7648 requires 2 feedback resistors R1 & R2 to control the output voltage. To set V OUT in the voltage mode, use the equation: R = VFB/IF where VFB is 0.8V in torch mode and 0.288V in flash mode, IF is the operating current of the LED. To set the operating current to be about 200mA in torch mode, the flash pin is forced low, R2 is selected as 0.8V/ 0.2 = 4Ω, as shown in the typical application circuit. To set the operating current to 700mA in flash mode, the flash pin is forced high, R is selected as 0.288V/0.41Ω = 700mA. In reality R in Flash includes the series MOSFET RDSON and the parallel combination of R2 = 4Ω shown by the formula: R1 = [(VOUT/0.8)-1]xR2 where flash < 0.4V, R1 = [(VOUT/0.288)-1]xR2 where flash > 1.0V. USING THE RLIM FUNCTION The peak inductor current, IPEAK, is programmed externally by the RLIM resistor connected between the RLIM pin and GND. The peak inductor current is defined by: R in Flash = (R1 x (R2+ Q1RDSON)) / (R1+ R2 + Q1RDSON) IPEAK = 1600/RLIM The saturation current specified for the inductor needs to be greater than the peak current to avoid saturating the inductor, which would result in a loss in efficiency and could damage the inductor. The SP7648 evaluation board uses a RLIM value of 1KΩ for an IPEAK = 1.6A to allow the circuit to deliver up to 700mA for VIN = 3.3V and VOUT= 4.2V. Other © 2012 Exar Corporation If the SP7648 is powered up before the LED is plugged in, the circuit will bring the feed-back pin to ZeroV and the SP7648 has a feature to set the output voltage to be 5V. Once the LED is plugged in, the feedback pin will go up to 0.8V in torch mode or 0.288V in flash mode and begin to regulate. The output voltage will go from 5V to VF+VFB, where VF is the forward voltage of the LED. When the LED is open, the 9/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator feedback pin voltage will go to ZeroV and the output voltage will go to 5V which will protect the part from overvoltage at the output. optional 10KΩ potentiometer may also be used for dimming the LED current by varying the potentiometer between low brightness and full brightness. One approach to control LED brightness is to apply a PWM signal to the SHDN input of the SP7648. In this case, the output current will be equal to the product of VREF/R1 and the average duty cycle at the SHDN pin. An © 2012 Exar Corporation If the FB pin is pulled below 150mV the output will default to 5V defined by an internal resistor divider. 10/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator PACKAGE SPECIFICATION 10-PIN DFN © 2012 Exar Corporation 11/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator 10-PIN MSOP © 2012 Exar Corporation 12/13 Rev. 2.0.0 SP7648 Low Reference High Efficiency Boost Regulator REVISION HISTORY Revision Date 2.0.0 11/19/2012 Description Reformat of datasheet FOR FURTHER ASSISTANCE Email: customersupport@exar.com Exar Technical Documentation: http://www.exar.com/TechDoc/default.aspx? EXAR CORPORATION HEADQUARTERS AND SALES OFFICES 48720 Kato Road Fremont, CA 94538 – USA Tel.: +1 (510) 668-7000 Fax: +1 (510) 668-7030 www.exar.com NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however , is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. or its in all Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. © 2012 Exar Corporation 13/13 Rev. 2.0.0