SP6669 1.5MHZ, 600mA SYNCHRONOUS STEP DOWN CONVERTER FEATURES Up to 600mA Output Current Up to 95% Efficiency 1.5MHz Constant Frequency Operation Low Dropout Operation Mode: 100% Duty Cycle Output Voltages as low as 0.6V No Schottky Diode Required 200μA Quiescent Current (no load) Excellent Line and Load Transient Response Over-Temperature Protection 2.5V to 5.5V Input Voltage Range Lead Free SOT23-5 Package APPLICATIONS Cellular Phones Wireless Networking Digital Cameras Portable Media Players Bluetooth Devices Portable Instruments DESCRIPTION The SP6669 is a 600mA synchronous buck converter using a constant frequency current mode architecture with pulse width modulation (PWM) for low output voltage ripple and fixed frequency noise, a pulse skip mode (PSM) for light load efficiency and a LDO mode for 100% duty cycle. With a 2.5V to 5.5V input voltage range and a 1.5MHz switching frequency, the SP6669 allows the use of small surface mount inductors and capacitors ideal for battery powered portable applications. The internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. Low output voltages are easily supported with the 0.6V feedback reference voltage. The SP6669 is available in an adjustable output voltage version, using an external resistor divider circuit, as well as fixed output voltage versions of 1.2V, 1.5V and 1.8V. The SP6669 is available in a 5 pin SOT-23 package. TYPICAL APPLICATION CIRCUIT Rev G – 12/02/2008 SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 1/10 BLOCK DIAGRAM Fig.1: SP6669 Block Diagram PIN DESCRIPTION SOT23-5L Pin Number Name 1 EN 2 GND 3 SW Switching node. 4 VIN Power Supply Pin. Must be decoupled to ground with a 4.7µF or greater ceramic capacitor. VFB Adjustable Version Feedback Input Pin. Connect VFB to the center point of the resistor divider. 5 VOUT Rev G – 12/02/2008 Description Enable Pin. Do not leave the pin floating. VEN<0.4V: Shutdown mode VEN>1.2V: Device enabled Ground Signal Pin. Fixed Output Voltage Version, Output Voltage Pin. An internal resistive divider divides the output voltage down for comparison to the internal reference voltage. SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 2/10 ELECTRICAL CHARACTERISTICS Absolute Maximum Ratings These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may affect device reliability. All voltages are with respect to ground. Input Voltage VIN ..........................-0.3V to 6V EN VFB Voltage ............................ -0.3V to VIN SW Voltage.................... -0.3V to (VIN + 0.3V) PMOS Switch Source Current (DC) ........ 800mA NMOS Switch Sink Current (DC) ........... 800mA Peak Switch Sink and Source Current ....... 1.3A Operating Junction Temp. (Note 1)......... 125ºC Storage Temp. Range TSTG ....... -65ºC to 150ºC Lead Temperature (sold. 10s) TLEAD ........ 300ºC Thermal Resistance RθJA ............................................... 250ºC/W RθJC .................................................90ºC/W Note 1: TJ is a function of the ambient temperature TA and power dissipation PD (TJ= TA + PD x 250°C/W). Recommended Operating Conditions Operating Temperature TOP ....... -40ºC to 85 ºC Input voltage VIN......................... 2.5V to 5.5V VIN=3.6V, TA=25ºC, unless otherwise specified – Boldface characters apply over the full temperature range. Parameter Symbol Feedback Current IVFB Regulated Feedback Voltage VFB Reference Voltage Line Regulation Output Voltage Accuracy ΔVFB ΔVOVL Output Voltage Line Regulation ΔVOUT Output Voltage Load Regulation Quiescent Current (Note 2) Shutdown Current Oscillator Frequency IPK IQ ISHTDWN fosc EN Leakage Current 0.600 VIN=2.5V to 5.5V -3 Max Unit ±30 nA 0.612 V 0.4 %/V +3 % ΔVOVL = VOVL – VFB (Adj.) 20 50 80 mV ΔVOVL = VOVL – VOUT (Fixed) 2.5 7.8 13 % 0.4 %/V VIN=2.5V to 5.5V VIN=3V, VFB=0.5V or VOUT=90%, Duty cycle <35% VFB=0.5V or VOUT=90% A 0.5 % 200 VEN=0V, VIN=4.2V VFB=0.6V or VOUT=100% 1.0 1.2 340 µA 0.1 1 µA 1.5 1.8 MHz 290 ISW=100mA 0.45 0.55 Ω RNFET ISW=100mA 0.40 0.50 Ω ILSW VEN=0V, VSW=0V or 5V, VIN=5V ±1 µA 1.2 V ±1 µA RDS(ON) of NMOS Shutdown Threshold 0.588 Typ. VFB=0V or VOUT=0V RPFET Enable Threshold Min VLOADREG RDS(ON) of PMOS SW Leakage TA=25°C ΔVOUT% Output Over-Voltage Lockout Peak Inductor Current Conditions VEN IEN kHz 0.4 V Note 1: The Switch Current Limit is related to the Duty Cycle. Please refer to figure 15 for details. Note 2: Dynamic quiescent current is higher due to the gate charge being delivered at the switching frequency. Rev G – 12/02/2008 SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 3/10 ELECTRICAL CHARACTERISTICS Typical Characteristics Fig. 2: Efficiency vs Output Current (mA) Fig. 3: Efficiency vs Output Current (mA) Fig. 4: Efficiency vs Output Current (mA) Fig. 5: Efficiency vs Output Current (mA) Fig. 6: Output Voltage vs Load Current Fig. 7: Reference Voltage vs Temperature Rev G – 12/02/2008 SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 4/10 ELECTRICAL CHARACTERISTICS Fig. 8: RDS(ON) vs Temperature Fig. 9: RDS(ON) vs Input Voltage Fig. 10: Dynamic Supply Current vs Temperature Fig. 11: Dynamic Supply Current vs Supply Voltage Fig. 12: Oscillator Frequency vs Temperature Fig. 13: Oscillator Frequency vs Supply Voltage Rev G – 12/02/2008 SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 5/10 ELECTRICAL CHARACTERISTICS Fig. 14: Discontinuous Operation Fig. 15: Start-up from Shutdown Fig. 16: Load Step Fig. 17: Load Step Fig. 17: Load Step Fig. 18: Load Step Rev G – 12/02/2008 SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 6/10 THEORY OF OPERATION Detailed Description Applications The typical application circuit of the adjustable output voltage option and the fixed output voltage option are shown below. The ESR rating of the capacitor is an important parameter to select COUT. The output ripple VOUT is determined by: ⎛ Eq. 3: ΔVOUT ≅ ΔI L ⎜⎜ ESR + ⎝ Fig. 18: Adjustable Output Voltage Version Typical Application Circuit 1 8 ⋅ f ⋅ COUT ⎞ ⎟⎟ ⎠ 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. Output Voltage – Adjustable Version Fig. 19: Fixed Output Voltage Version Typical Application Circuit ⎛ Inductor Selection Inductor ripple current and core saturation are two factors considered to select the inductor value. Eq. 1: ΔI L = ⎛ V 1 VOUT ⎜⎜1 − OUT f ⋅L VIN ⎝ ⎞ ⎟⎟ ⎠ Equation 1 shows the inductor ripple current as a function of the frequency, and VOUT. It is inductance, VIN 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: I RMS ≅ I OMAX Rev G – 12/02/2008 The adjustable output voltage version is determined by: VOUT (VIN − VOUT ) VIN R ⎞ Eq. 4: VOUT = 0.6V ⋅ ⎜⎜1 + 2 ⎟⎟ ⎝ R1 ⎠ Thermal Considerations Allthough the SP6669 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. PCB Layout The following PCB layout guidelines should be taken into account to ensure proper operation and performance of the SP6669: 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. SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 7/10 THEORY OF OPERATION 4- The SW and VFB nodes should be kept as separate as possible to minize possible effects from the high frequency and voltage swings of the SW node. 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. 5- The ground plates of CIN and COUT should be kept as close as possible. The inductor value needed can be calculated using the following equation Ouptut Voltage Ripple for VIN close to VOUT When the input voltage VIN is close to the the SP6669 output voltage VOUT, transitions smoothly from the switching PWM converter mode into a LDO mode. The following diagram shows the output voltage ripple versus the input voltage for a 3.3V output setting and a 200mA current load. Design Example L= ⎛ V 1 VOUT ⎜⎜1 − OUT f ⋅ ΔI L VIN ⎝ ⎞ ⎟⎟ ⎠ VIN=4.2V, Subsituting VOUT=1.8V, ΔIL=240mA and f=1.5MHz gives L = 2.86μH A 2.2µH inductor can be choosen 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. Fig.20: VOUT Ripple Voltage for VIN decreasing close to VOUT Rev G – 12/02/2008 SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 8/10 PACKAGE SOT23-5L Unit: mm Rev G – 12/02/2008 SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 9/10 ORDERING INFORMATION Adjustable Output Voltage Version Part Number SP6669AEK-L/TRR3 Voltage Option Adjustable Operating Temperature Range -40ºC to +85ºC Package Marking SOT23-5 QBWW Package Marking SOT23-5 SOT23-5 SOT23-5 RBWW SBWW TBWW Packing Quantity 3,000/T&R “WW” = Work Week Fixed Output Voltage Version Part Number SP6669BEK-L/TRR3 SP6669CEK-L/TRR3 SP6669DEK-L/TRR3 Voltage Option 1.2V 1.5V 1.8V Operating Temperature Range -40ºC to +85ºC -40ºC to +85ºC -40ºC to +85ºC Packing Quantity 3,000/T&R 3,000/T&R 3,000/T&R “WW” = Work Week Note that the SP6669 series is packaged in Tape and Reel with a reverse part orientation as per the following diagram 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 or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all 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. 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 Rev G – 12/02/2008 SP6669 1.5MHz 0.6A Sync. Step Down Converter © 2008 Exar Corporation 10/10