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| X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter July 2009 Rev. 1.0.0 GENERAL DESCRIPTION The XRP6657 is a high efficiency synchronous step down DC to DC converter capable of delivering up to 1.5 Amp of current and optimized for portable battery-operated applications. Operating over an input voltage range of 2.5V to 5.5V, it provides an adjustable regulated output voltage down to 0.6V. The XRP6657 uses a constant 1.3 MHz frequency pulse width modulation (PWM) scheme allowing for compact external components, low output voltage ripple and fixed frequency noise, while Pulse Skip Mode (PSM) is used to improve light load efficiency. A low dropout mode provides 100% duty cycle operation. The solution footprint is further reduced by a current mode internal compensation network and built-in synchronous switch removing the need for an external Schottky. Over-current and over-temperature protection insures safe operations under abnormal operating conditions. The XRP6657 is available in a compact RoHS compliant "green"/halogen free thin 6-pin DFN package. APPLICATIONS * Point of Loads * Set-Top Boxes * Portable Media Players * Hard Disk Drives FEATURES * Guaranteed 1.5A Output Current - Fixed 1.3MHz Frequency PWM Operations - Up to 95% efficiency - Input Voltage: 2.5V to 5.5V * Adjustable Output Voltage * Internal Compensation Network * No Schottky Diode Required * LDO Operation: 100% Duty Cycle * 240A Quiescent Current (no load) * 1A Shutdown Current * Soft Start Function * Over-current/Over-temperature Protection * "Green"/Halogen Free DFN-6 Package TYPICAL APPLICATION DIAGRAM Fig. 1: XRP6657 Application Diagram Exar Corporation 48720 Kato Road, Fremont CA 94538, USA www.exar.com Tel. +1 510 668-7000 - Fax. +1 510 668-7001 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter ABSOLUTE MAXIMUM 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 VIN ....................................... -0.3V to 6.0V EN, VFB Voltage ........................................... -0.3V to VIN SW Voltage ...................................... -0.3V to (VIN+0.3V) PMOS Switch Source Current (DC) .............................. 2A NMOS Switch Sink Current (DC) ................................. 2A Peak Switch Sink and Source Current....................... 3.5A Junction Temperature TJ1,2 .................................... 125C Lead Temperature (Soldering, 10 sec) ................... 260C Storage Temp. Range TSTG ....................... -65C to 150C ESD Rating (HBM - Human Body Model) .................... 2kV ESD Rating (MM - Machine Model) ...........................200V OPERATING RATINGS Input Voltage Range VIN ............................... 2.5V to 5.5V Ambient Temperature Range TA ................. -40C to 85C Thermal Resistance JC ...................................... 10C/W Thermal Resistance JA ...................................... 55C/W Note 1: TJ is a function of the ambient temperature TA and power dissipation PD (TJ= TA + PD x 55C/W). Note 2:XRP6657 has a build-in temperature protection circuitry to avoid damages from overload conditions. ELECTRICAL SPECIFICATIONS Specifications with standard type are for an Operating Junction Temperature of TA = 25C 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 TA = 25C, and are provided for reference purposes only. Unless otherwise indicated, VIN = 5.0V, TA= 25C. Parameter Feedback Current IVFB Regulated Feedback Voltage VFB Reference Voltage Line Regulation VFB Output Voltage Accuracy VOUT% Output Over-Voltage Lockout VOVL Output Voltage Line Regulation VOUT Peak Inductor Current IPK Output Voltage Load Regulation VLOADREG Quiescent Current I 2 Q Min. 0.588 0.585 Typ. 0.600 0.600 Max. 100 0.612 0.615 0.4 Units nA V %/V % mV %/V A %/V * TA = 25C * * * Conditions -40C TA 85C -3 20 50 3 80 0.4 2.4 0.2 240 0.1 340 1 1.56 VOVL = VOVL - VFB VIN = 2.5V to 5.5V VIN=3V, VFB=0.5V or VOUT=90%, duty cycle<35% IOUT=10mA to 1.5A VFB=0.5V or VOUT=90% VEN=0V, VIN=4.2V * VFB=0.6V or VOUT=100% ISW=750mA ISW=-750mA VEN=0V, VSW=0V or 5V, VIN=5V * * * A A MHz % Shutdown Current ISHTDWN Oscillator Frequency fOSC Minimum Duty Cycle DMIN RDS(ON) of PMOS RPFET RDS(ON) of NMOS RNFET SW Leakage ILSW Enable Threshold VEN Shutdown Threshold VEN EN Leakage Current IEN 0.4 1.04 1.3 20 0.18 0.16 1 1.2 1 A V V A Note 1: The Switch Current Limit is related to the Duty Cycle. Please refer to figure 29 for details. Note 2: Dynamic quiescent current is higher due to the gate charge being delivered at the switching frequency. (c) 2009 Exar Corporation 2/11 Rev. 1.0.0 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter BLOCK DIAGRAM Fig. 2: XRP6657 Block Diagram PIN ASSIGNEMENT Fig. 3: XRP6657 Pin Assignment (Top View) (c) 2009 Exar Corporation 3/11 Rev. 1.0.0 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter PIN DESCRIPTION Name VFB VSS_PWR SW VIN_PWR VIN_CLN Pin Number 1 2 3 4 5 Description Feedback Pin. Receives the feedback voltage from an external resistive divider across the output. Power Ground Pin. Switching node. Must be connected to inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches. Power Input Pin. Must be closely decoupled to ground pin with a 4.7F or greater capacitor. Analog Input Pin. Must be closely decoupled to ground pin with a 4.7F or greater capacitor. Enable Pin. >1.2V: Enables the XRP6657 <0.4V:Disables the XRP6657 Do not leave this pin floating and enable the device once Vin is in the operating range. Analog Ground Pin. EN VSS_CLN 6 Exposed Pad ORDERING INFORMATION Part Number XRP6657IHBTR-F XRP6657EVB Temperature Range -40CTA+85C Marking Package Packing Quantity Note 1 Note 2 Adjustable output voltage 6657 IHB WWX XRP6657 Evaluation Board RoHS compliant Thin DFN-6L 5K/Tape and Reel Halogen Free "WW" = Work Week - "X" = Lot Number (c) 2009 Exar Corporation 4/11 Rev. 1.0.0 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter TYPICAL PERFORMANCE CHARACTERISTICS All data taken at VIN = 2.7V to 5.5V, TJ = TA = 25C, unless otherwise specified - Schematic and BOM from Application Information section of this datasheet. Fig. 4: Efficiency vs Output Current VOUT=3.3V Fig. 5: Efficiency vs Output Current VOUT=1.8V Fig. 6: Efficiency vs Output Current VOUT=1.5V Fig. 7: Efficiency vs Output Current VOUT=1.2V Fig. 8: Reference Voltage vs Temperature Fig. 9: Output Voltage vs Load Current (c) 2009 Exar Corporation 5/11 Rev. 1.0.0 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter Fig. 10: PMOS RDS(ON) vs Temperature Fig. 11: NMOS RDS(ON) vs Temperature Fig. 12: PMOS RDS(ON) vs Supply Voltage Fig. 13: NMOS RDS(ON) vs Temperature Fig. 14: Dynamic Supply Current vs Temperature Fig. 15: Dynamic Supply Current vs Supply Voltage (c) 2009 Exar Corporation 6/11 Rev. 1.0.0 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter Fig. 16: Switching Frequency vs Temperature Fig. 17: Switching Frequency vs Supply Voltage Fig. 18: Start-Up from Shutdown Fig. 19: Start-Up from Shutdown Fig. 20: Load Step Fig. 21: Load Step (c) 2009 Exar Corporation 7/11 Rev. 1.0.0 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter THEORY OF OPERATION The typical application circuit is shown below. OUTPUT VOLTAGE The adjustable output voltage is determined by: Eq. 4: 0.6 1 SHORT CIRCUIT BEHAVIOR The XRP6657 has an over current and over temperature protection. The over current applies cycle by cycle and limits the P-driver FET current to maintain the inductor current within safe limits. The over temperature protection circuitry turns off the driver FETs when the junction temperature is too high. Normal Operations are restored when temperature drops below the safety threshold. In the following example, the XRP6657 is used to convert a 5V input to a 1.2V output. Shorting VOUT to ground triggers both the over current and over temperature protection circuits. The waveform is shown below. Fig. 22: Typical Application Circuit INDUCTOR SELECTION Inductor ripple current and core saturation are two factors considered to select the inductor value. Eq. 1: 1 Equation 1 shows the inductor ripple current as a function of the frequency, inductance, VIN and VOUT. It is recommended to set the ripple current to 40% of the maximum load current. A low ESR inductor is preferred. CIN AND COUT SELECTION A low ESR input capacitor can prevent large voltage transients at VIN. The RMS current rating of the input capacitor is required to be larger than IRMS calculated by: Eq. 2: The ESR rating of the capacitor is an important parameter to select COUT. The output ripple VOUT is determined by: Eq. 3: Fig. 23: Short Circuit Response Higher values, lower cost ceramic capacitors are now available in smaller sizes. These capacitors have high ripple currents, high voltage ratings and low ESR that makes them ideal for switching regulator applications. As COUT does not affect the internal control loop stability, its value can be optimized to balance very low output ripple and circuit size. It is recommended to use an X5R or X7R rated capacitors which have the best temperature and voltage characteristics of all the ceramics for a given value and size. (c) 2009 Exar Corporation 8/11 THERMAL CONSIDERATIONS Although the XRP6657 has an on board over temperature circuitry, the total power dissipation it can support is based on the package thermal capabilities. The formula to ensure safe operation is given in note 1 under the operating ratings section. To avoid exceeding the maximum junction temperature, thermal analysis is strongly suggested. Rev. 1.0.0 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter PCB LAYOUT The following PCB layout guidelines should be taken into account to ensure proper operation and performance of the XRP6657: 1- The GND, SW and VIN traces should be kept short, direct and wide. 2- VFB pin must be connected directly to the feedback resistors. The resistor divider network must be connected in parallel to the COUT capacitor. 3- The input capacitor CIN must be kept as close as possible to the VIN pin. 4- The SW and VFB nodes should be kept as separate as possible to minimize possible effects from the high frequency and voltage swings of the SW node. 5- The ground plates of CIN and COUT should be kept as close as possible. 6- Connect all analog grounds to a common node and connect the common node to the power ground via an independent path. voltage. The transition from PWM mode to LDO mode is smooth. Figure 24 illustrates the amount of output voltage ripple for an output voltage of 3.3V providing 200mA. Fig. 24: Output Voltage Ripple in LDO mode DESIGN EXAMPLE In a single Lithium-Ion battery powered application, the VIN range is about 2.7V to 4.2V. The desired output voltage is 1.8V. The inductor value needed can be calculated using the following equation 1 1 SELF ENABLE APPLICATION A self Enable function is easily implemented through the following arrangement. Substituting VOUT=1.8V, VIN=4.2V, IL=600mA and f=1.3MHz gives 1.32 A 1.5H inductor can be chosen with this application. An inductor of greater value with less equivalent series resistance would provide better efficiency. The CIN capacitor requires an RMS current rating of at least ILOAD(MAX)/2 and low ESR. In most cases, a ceramic capacitor will satisfy this requirement. See recommended components section below A resistor ratio R3/R4=1/1.5 is recommended. OUTPUT VOLTAGE RIPPLE IN LDO MODE The XRP6657 enters the LDO mode when input voltage is close to the selected output RECOMMENDED COMPONENTS Supplier Inter-Technical Supplier Murata Murata Inductance 1.5H Capacitance 4.7F 22F ISAT 2.5A DCRMAX 47m Package 0805 0805 Dimensions (mm) 4.5x5x2 Part # SD52-1R5M Part # GRM219R61A475K GRM219R60J226M (c) 2009 Exar Corporation 9/11 Rev. 1.0.0 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter PACKAGE SPECIFICATION THIN DFN-6L (c) 2009 Exar Corporation 10/11 Rev. 1.0.0 X RP 6 6 5 7 1.5A 1.3MHz Synchronous Step Down Converter REVISION Revision 1.0.0 Date 07/14/2009 First release of data sheet Description FOR FURTHER ASSISTANCE Email: Exar Technical Documentation: customersupport@exar.com 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. Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. or its in all (c) 2009 Exar Corporation 11/11 Rev. 1.0.0 |
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