(R) SP7652 Preliminary Wide Input Voltage Range 6A, 600kHz, Buck Regulator SP7652 FEATURES DFN PACKAGE 7mm x 4mm 2.5V to 28V Step Down Achieved Using Dual Input Output Voltage down to 0.8V 6A Output Capability (Up to 8A with Air Flow) Built in Low RDSON Power FETs (15 m typ) Highly Integrated Design, Minimal Components 600 kHz Fixed Frequency Operation UVLO Detects Both VCC and VIN Over Temperature Protection Short Circuit Protection with Auto-Restart Wide BW Amp Allows Type II or III Compensation Programmable Soft Start Fast Transient Response High Efficiency: Greater than 92% Possible Asynchronous Start-Up into a Pre-Charged Output Small 7mm x 4mm DFN Package PGND 1 26 LX TOP VIEW PGND 2 Heatsink Pad 1 Connect to Lx PGND 3 25 LX 24 LX GND 4 23 LX VFB 5 2 2 VCC COMP 6 21 GND Heatsink pad 2 Connect to GND UVIN 7 20 GND GND 8 19 GND SS 9 18 BST VIN 10 17 NC Heatsink pad 3 Connect to VIN VIN 11 16 LX VIN 12 15 LX VIN 13 14 LX Now Available in Lead Free Packaging DESCRIPTION The SP7652 is a synchronous step-down switching regulator optimized for high efficiency. The part is designed to be especially attractive for dual supply, 12V step down with 5V used to power the controller. This lower VCC voltage minimizes power dissipation in the part. The SP7652 is designed to provide a fully integrated buck regulator solution using a fixed 600kHz frequency, PWM voltage mode architecture. Protection features include UVLO, thermal shutdown and output short circuit protection. The SP7652 is available in the space saving DFN package. TYPICAL APPLICATION CIRCUIT 100pF 21.5k,1% RSET (note 2) U1 1nF 12K 2 3 4 5 6 7 CF1 100pF 8 9 ENABLE 10 CSS 22nF VIN VOUT 3.3V 0-8A 68.1k,1% SP7652 1 22pF 5.1K 11 12 13 PGND LX PGND LX PGND LX GND LX VFB VCC COMP GND UVIN GND GND GND SS BST VIN NC VIN LX VIN LX VIN LX 26 25 1.5uH, Irate=8A 47uF 24 Ceramic X5R 6.3V 23 5V VCC 22 21 20 CVCC 1uF 19 18 17 5.1 SD101AWS 16 15 14 1uF 2.5V - 20V Notes: C1 22uF 1. U1 Bottom-Side Layout should has three contacts isolated from one another VIN and SWNODE and GND 2. RSET = 54.48 / (Vout - 0.8V) (kOhm) GND Date: 08/12/04 SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator 1 (c) Copyright 2004 Sipex Corporation 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. GH ......................................................................... -0.3V to BST+0.3V GH-SWN ......................................................................................... 7V All other pins .......................................................... -0.3V to VCC+0.3V VCC .................................................................................................. 7V VIN ........................................................................................................................................... 30V ILX ............................................................................................................................................ 10A BST ............................................................................................... 35V BST-SWN ......................................................................... -0.3V to 7V SWN ................................................................................... -1V to 30V Storage Temperature .................................................. -65C to 150C Power Dissipation .................................................... Internally Limited Lead Temperature (Soldering, 10 sec) ...................................... 300C ESD Rating .......................................................................... 2kV HBM Thermal Resistance JC .................................................................................... 5C/W ELECTRICAL SPECIFICATIONS Unless otherwise specified: -40C < TAMB < 85C, -40C R2 = R1 / [ ( Vout / 0.80V ) - 1 ] Where R1 = 68.1K and for Vout = 0.80V setting, simply remove R2 from the board. Furthermore, one could select the value of R1 and R2 combination to meet the exact output voltage setting by restricting R1 resistance range such that 50K < R1 < 100K for overall system loop stability. SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator 6 (c) Copyright 2004 Sipex Corporation APPLICATIONS INFORMATION saturate at the peak inductor current Inductor Selection There are many factors to consider in selecting the inductor including core material, inductance vs. frequency, current handling capability, efficiency, size and EMI. In a typical SP7652 circuit, the inductor is chosen primarily by operating frequency, saturation current and DC resistance. Increasing the inductor value will decrease output voltage ripple, but degrade transient response. Low inductor values provide the smallest size, but cause large ripple currents, poor efficiency and more output capacitance to smooth out the larger ripple current. The inductor must be able to handle the peak current at the switching frequency without saturating, and the copper resistance in the winding should be kept as low as possible to minimize resistive power loss. A good compromise between size, loss and cost is to set the inductor ripple current to be within 20% to 40% of the maximum output current. I PEAK = I OUT (max) + and provide low core loss at the high switching frequency. Low cost powdered iron cores are inappropriate for 900kHz operation. Gapped ferrite inductors are widely available for consideration. Select devices that have operating data shown up to 1MHz. Ferrite materials, on the other hand, are more expensive and have an abrupt saturation characteristic with the inductance dropping sharply when the peak design current is exceeded. Nevertheless, they are preferred at high switching frequencies because they present very low core loss and the design only needs to prevent saturation. In general, ferrite or molypermalloy materials are better choice for all but the most cost sensitive applications. The switching frequency and the inductor operating point determine the inductor value as follows: L= I PP 2 Optimizing Efficiency The power dissipated in the inductor is equal to the sum of the core and copper losses. To minimize copper losses, the winding resistance needs to be minimized, but this usually comes at the expense of a larger inductor. Core losses have a more significant contribution at low output current where the copper losses are at a minimum, and can typically be neglected at higher output currents where the copper losses dominate. Core loss information is usually available from the magnetic vendor. Proper inductor selection can affect the resulting power supply efficiency by more than 15-20%! VOUT (V IN (max) - VOUT ) VIN (max) FS Kr I OUT ( max) where: Fs = switching frequency Kr = ratio of the ac inductor ripple current to the maximum output current The peak to peak inductor ripple current is: The copper loss in the inductor can be calculated using the following equation: I PP = VOUT (VIN (max) - VOUT ) PL( Cu) = I L2 ( RMS ) RWINDING VI N (max) FS L where IL(RMS) is the RMS inductor current that can be calculated as follows: Once the required inductor value is selected, the proper selection of core material is based on peak inductor current and efficiency requirements. The core must be large enough not to Date: 08/12/04 IL(RMS) = IOUT(max) 1 + 1 3 SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator 7 ( IPP IOUT(max) ) 2 (c) Copyright 2004 Sipex Corporation APPLICATIONS INFORMATION Output Capacitor Selection The required ESR (Equivalent Series Resistance) and capacitance drive the selection of the type and quantity of the output capacitors. The ESR must be small enough that both the resistive voltage deviation due to a step change in the load current and the output ripple voltage do not exceed the tolerance limits expected on the output voltage. During an output load transient, the output capacitor must supply all the additional current demanded by the load until the SP7652 adjusts the inductor current to the new value. FS = Switching Frequency D = Duty Cycle COUT = Output Capacitance Value Input Capacitor Selection The input capacitor should be selected for ripple current rating, capacitance and voltage rating. The input capacitor must meet the ripple current requirement imposed by the switching current. In continuous conduction mode, the source current of the high-side MOSFET is approximately a square wave of duty cycle VOUT/VIN. Most of this current is supplied by the input bypass capacitors. The RMS value of input capacitor current is determined at the maximum output current and under the assumption that the peak In order to maintain VOUT, the capacitance must be large enough so that the output voltage is held up while the inductor current ramps up or down to the value corresponding to the new load current. Additionally, the ESR in the output capacitor causes a step in the output voltage equal to the current. Because of the fast transient response and inherent 100% and 0% duty cycle capability provided by the SP7652 when exposed to output load transient, the output capacitor is typically chosen for ESR, not for capacitance value. to peak inductor ripple current is low, it is given by: ICIN(rms) = IOUT(max) D(1 - D) The worse case occurs when the duty cycle D is 50% and gives an RMS current value equal to IOUT/2. The output capacitor's ESR, combined with the inductor ripple current, is typically the main contributor to output voltage ripple. The maximum allowable ESR required to maintain a specified output voltage ripple can be calculated by: RESR Select input capacitors with adequate ripple current rating to ensure reliable operation. The power dissipated in the input capacitor is: 2 PCIN = ICIN ( rms ) R ESR ( CIN ) VOUT IPK-PK This can become a significant part of power losses in a converter and hurt the overall energy transfer efficiency. The input voltage ripple primarily depends on the input capacitor ESR and capacitance. Ignoring the inductor ripple current, the input voltage ripple can be determined by: where: VOUT = Peak to Peak Output Voltage Ripple IPK-PK = Peak to Peak Inductor Ripple Current The total output ripple is a combination of the ESR and the output capacitance value and can be calculated as follows: ( VOUT = IPP (1 - D) COUTFS Date: 08/12/04 ) 2 + (IPPRESR)2 SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator 8 (c) Copyright 2004 Sipex Corporation APPLICATIONS INFORMATION VIN = I out (max) RE SR (CIN ) + High cross over frequency is desirable for fast transient response, but often jeopardizes the system stability. Cross over frequency should be higher than the ESR zero but less than 1/5 of the switching frequency. The ESR zero is contributed by the ESR associated with the output capacitors and can be determined by: I OUT ( MAX )VOUT (VI N - VOUT ) FS C INV IN 2 The capacitor type suitable for the output capacitors can also be used for the input capacitors. However, exercise extra caution when tantalum capacitors are used. Tantalum capacitors are known for catastrophic failure when exposed to surge current, and input capacitors are prone to such surge current when power supplies are connected "live" to low impedance power sources. 1 Z(ESR) = 2 COUT RESR Loop Compensation Design The next step is to calculate the complex conjugate poles contributed by the LC output filter, The open loop gain of the whole system can be divided into the gain of the error amplifier, PWM modulator, buck converter output stage, and feedback resistor divider. In order to cross over at the selected frequency FCO, the gain of the error amplifier has to compensate for the attenuation caused by the rest of the loop at this frequency. 2 Type III Voltage Loop Compensation GAMP (s) Gain Block + _ L COUT When the output capacitors are of a Ceramic Type, the SP7652 Evaluation Board requires a Type III compensation circuit to give a phase boost of 180 in order to counteract the effects of an under damped resonance of the output filter at the double pole frequency. The goal of loop compensation is to manipulate loop frequency response such that its gain crossesover 0db at a slope of -20db/dec. The first step of compensation design is to pick the loop cross over frequency. VREF (Volts) 1 P(LC) = PWM Stage GPWM Gain Block Output Stage GOUT (s) Gain Block VIN (SRz2Cz2+1)(SR1Cz3+1) (SRESRCOUT+ 1) VRAMP_PP SR1Cz2(SRz3Cz3+1)(SRz2Cp1+1) [S^2LCOUT+S(RESR+RDC) COUT+1] VOUT (Volts) Notes: RESR = Output Capacitor Equivalent Series Resistance. RDC = Output Inductor DC Resistance. VRAMP_PP = SP6132 Internal RAMP Amplitude Peak to Peak Voltage. Condition: Cz2 >> Cp1 & R1 >> Rz3 Output Load Resistance >> RESR & RDC Voltage Feedback GFBK Gain Block R2 VFBK (Volts) (R1 + R2) or VREF VOUT SP7652 Voltage Mode Control Loop with Loop Dynamic Definitions: RESR = Output Capacitor Equivalent Series Resistance RDC = Output Inductor DC Resistance RRAMP_PP = SP7652 internal RAMP Amplitude Peak to Peak Voltage Conditions: CZ 2 >> Cp1 and R1 >> RZ 3 Output Load Resistance >> RESR and RDC Date: 08/12/04 SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator 9 (c) Copyright 2004 Sipex Corporation APPLICATIONS INFORMATION Gain (dB) Error Amplifier Gain Bandwidth Product Condition: C22 >> CP1, R1 >> RZ3 1/6.28 (RZ3) (CZ3) 1/6.28 (RZ2) (CP1) 1/6.28 (R1) (CZ2) 1/6.28 (R1) (CZ3) 1/6.28(R22) (CZ2) 20 Log (RZ2/R1) Frequency (Hz) Bode Plot of Type III Error Amplifier Compensation. CP1 RZ3 CZ3 CZ2 RZ2 VOUT R1 68.1k, 1% 5 VFB R SET + + - 0.8V R SET 6 COMP CF1 =54.48/ (VOUT -0.8) (k) Type III Error Amplifier Compensation Circuit Date: 08/12/04 SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator 10 (c) Copyright 2004 Sipex Corporation TYPICAL PERFORMANCE CHARACTERISTICS SP7652 Effi. vs Iout Plots @ Vin=8V, 12V, 15V, and Vout=5.0V 96.0 SP7652 Vout vs Iout Plots @ Vin=8V, 12V, and 15V 4.96 Output Voltage (V) 94.0 Efficiency (%) 92.0 90.0 88.0 86.0 Vin=12V Vin=8V Vin=15V 84.0 82.0 4.955 4.95 Vin=12V Vin=8V Vin=15V 4.945 4.94 80.0 1 2 3 4 5 0 6 1 2 SP7652 Effi. vs Iout Plots @ Vin=5V, and Vout=3.3V 93.5 5 6 3.305 Output Voltage (V) Efficiency (%) 4 SP7652 Vout vs Iout Plots @ Vin=5V, and Vout=3.3V 3.31 93.0 92.5 92.0 91.5 91.0 90.5 3.3 3.295 3.29 3.285 90.0 1 2 3 4 5 3.28 6 0 Load Current (A) 1 2 3 4 5 6 Load Current (A) SP7652 Effi. vs Iout Plots @ Vin=3.3V, and Vout=0.8V SP7652 Vout vs Iout Plots @ Vin=3.3V, and Vout=0.8V 80.0 79.0 0.794 Output Voltage (V) 78.0 Efficiency (%) 3 Load Current (A) Load Current (A) 77.0 76.0 75.0 74.0 73.0 72.0 0.792 0.79 0.788 71.0 0.786 70.0 1 2 3 4 5 0 6 1 Date: 08/12/04 2 3 4 5 6 Load Current (A) Load Current (A) SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator 11 (c) Copyright 2004 Sipex Corporation PACKAGE: 26 PIN DFN D (7 x 4 mm) E Top View A A3 A1 Side View b e L E2 D2 D2 D3 26 Pin DFN SYMBOL A A1 A3 b D D2 D3 e E E2 L Bottom View DIMENSIONS in (mm) MIN NOM MAX 0.800 0.850 0.900 0.000 - 0.050 0.178 0.203 0.228 0.17 0.22 0.27 6.95 7.05 7.00 2.05 2.10 1.78 1.83 1.88 2.00 0.45 0.50 0.55 3.95 4.00 4.05 2.730 2.780 2.830 0.350 0.400 0.450 26 Pin DFN Date: 08/12/04 SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator 12 (c) Copyright 2004 Sipex Corporation ORDERING INFORMATION Part Number Temperature Package SP7652ER/TR ......................................... -40C to +85C ................................. 26 Pin 7 X 4 DFN SP7652ER-L/TR ..................................... -40C to +85C ............. (Lead Free) 26 Pin 7 X 4 DFN /TR = Tape and Reel Pack quantity is 3000 DFN. Corporation ANALOG EXCELLENCE Sipex Corporation Headquarters and Sales Office 233 South Hillview Drive Milpitas, CA 95035 TEL: (408) 934-7500 FAX: (408) 935-7600 Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. Date: 08/12/04 SP7652 Wide Input Voltage Range 6A, 600kHz, Buck Regulator 13 (c) Copyright 2004 Sipex Corporation