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| SP7655 Evaluation Board Manual Easy Evaluation for the SP7655ER 24V Input, 0 to 8A Output Synchronous Buck Converter Built in Low Rds(on) Power FETs UVLO Detects Both VCC and VIN High Integrated Design, Minimal Components High Efficiency: 85% Feature Rich: UVIN, Programmable Softstart, External VCC Supply and Output Dead Short Circuit Shutdown SP7655EB SCHEMATIC U1 SP7655 1 PGND PGND PGND GND VFB COMP UVIN GND SS VIN VIN VIN VIN LX LX LX LX VCC GND GND GND BST NC LX LX LX 26 25 24 23 22 21 20 19 18 17 16 15 14 2 3 4 5 6 7 8 9 L1 IHLP-2525CZ-01-2R2MTR 2.2uH, Irate=8A DCR=10.4mOhm C3 47uF 6.3V CVCC 2.2uF DBST SD101AWS CBST 1uF CZ2 RZ2 2,200pF 7.68k,1% CP1 15pF fs=300Khz RZ3 8.66k,1% CZ3 120pF VOUT 3.30V 0-8A R1 68.1k,1% CF1 100pF GND2 C3 CERAMIC 1210 X5R R2 21.5k,1% CSS 47nF 10 11 12 VIN 24V C1,C4 CERAMIC 1210 Y5V C1 3.3uF 50V C4 3.3uF 50V 13 R3 499k,1% D1 1 U2 SPX5205 VIN VOUT GND EN BYP 4 5 2 3 Notes: U1 Bottom-Side Layout should hhree Contacts which t isolated from one of another, QTQB Drain Contact & d Controller GND C t All tresistor & capacitor i 0603 unless other wise MMSZ4678T1 Vz=12V R4 100k,1% C2 0.1uF GND Date: 2/01/05 SP7655 Evaluation Manual Copyright 2004 Sipex Corporation USING THE EVALUATION BOARD 1) Powering Up the SP7655EB Circuit Connect the SP7655 Evaluation Board with an external +24V power supply. Connect with short leads and large diameter wire directly to the "VIN" and "GND" posts. Connect a Load between the VOUT and GND2 posts, again using short leads with large diameter wire to minimize inductance and voltage drops. 2) Measuring Output Load Characteristics VOUT ripple can best be seen touching probe tip to the pad for C3 and scope GND collar touching GND side of C3 using short wrapped wire around collar - avoid a GND lead on the scope which will increase noise pickup. 3) Using the Evaluation Board with Different Output Voltages While the SP7655 Evaluation Board has been tested and delivered with the output set to 3.30V, by simply changing one resistor, R2, the SP7655 can be set to other output voltages. The relationship in the following formula is based on a voltage divider from the output to the feedback pin VFB, which is set to an internal reference voltage of 0.80V. Standard 1% metal film resistors of surface mount size 0603 are recommended. Vout = 0.80V (R1 / R2 + 1 ) => 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. Note that since the SP7655 Evaluation Board design was optimized for 24V down conversion to 3.30V, changes of output voltage and/or input voltage will alter performance from the data given in the Power Supply Data section. In addition, the SP7655ER provides short circuit protection by sensing Vout at GND. POWER SUPPLY DATA The SP7655ER is designed with a very accurate 1.0% reference over line, load and temperature. Figure 1 data shows a typical SP7655 Evaluation Board Efficiency plot, with efficiencies to 85% (Including generation of 5V Vcc) and output currents to 8A. SP7655ER Load Regulation is shown in Figure 2 of only 1% change in output voltage from 0.5A load to 8A load. Figures 3 and 4 illustrate a 5A to 8A and 0A to 6A Load Step. Start-up Response in Figures 5, 6 and 7 show a controlled start-up with different output load behavior when power is applied where the input current rises smoothly as the Softstart ramp increases. In Figure 8 the SP7655ER is configured for hiccup mode in response to an output dead short circuit condition and will Softstart until the over-load is removed. Figure 9 and 10 show output voltage ripple less than 135mV at no load to 8A load. While data on individual power supply boards may vary, the capability of the SP7655ER of achieving high accuracy over a range of load conditions shown here is quite impressive and desirable for accurate power supply design. 2 Efficiency vs Load (24V to 3.3V) Output Voltage (Vdc) 0.5 1 2 3 4 6 8 100.00 90.00 80.00 70.00 60.00 Load Current (A) Load Regulation (24V to 3.3V) 3.340 3.320 3.300 3.280 3.260 0.5 1 2 3 4 6 8 Output Current (A) Figure 1. Efficiency vs Load Vout Efficiency % Figure 2. Load Regulation Vout Iout (2A/div) Iout (2A/div) Figure 3. Load Step Response: 5->8A Vout Figure 4. Load Step Response: 0->6A Vout Vin SoftStart Vin SoftStart Iout (2A/div) Iout (2A/div) Figure 5. Start-Up Response: No Load Figure 6. Start-Up Response: 3.0A Load Vout SoftStart Vin SoftStart Vout Iout (5A/div) Ichoke (10A/div) Figure 7. Start-Up Response: 8A Load Figure 8. Output Load Short Circuit 3 Vout ripple = 100mV Vout ripple = 134mV Ichoke (5A/div) Ichoke (5A/div) Figure 9. Output Ripple: No Load Load Figure 10. Output Ripple: 8A TYPE III LOOP COMPENSATION DESIGN The open loop gain of the SP7655EB can be divided into the gain of the error amplifier Gamp(s), PWM modulator Gpwm, buck converter output stage Gout(s), and feedback resistor divider Gfbk. In order to crossover at the selecting frequency fco, the gain of the error amplifier has to compensate for the attenuation caused by the rest of the loop at this frequency. The goal of loop compensation is to manipulate the open loop frequency response such that its gain crosses over 0dB at a slope of -20dB/dec. The open loop crossover frequency should be higher than the ESR zero of the output capacitors but less than 1/5 to 1/10 of the switching frequency fs to insure proper operation. Since the SP7655EB is designed with Ceramic Type output capacitors, a Type III compensation circuit is required to give a phase boost of 180 in order to counteract the effects of the output LC under damped resonance double pole frequency. 4 Type III Voltage L Compensation Gamp(S) Gain Block Vref (Volts ) (SRz2Cz2+1)(SR1Cz 3+1) SR1Cz2(SRz3Cz3+1)(SRz2C 1+1) PWM Stage Gpwm Gain Block Vin Vramp_p Output Stage Gout(S) Gain Block (SResrCout+ 1) [S^2LCout+S(Resr+Rdc)Co t+1] Vout (Volts ) Voltage Feedback Gfbk Gain Block R2 Vref OR (R1+R2 Vout ) Definition Resr Rdc Vfbk (Volts ) := Output Capacitor Equivalent Series Resitance := Output Inductor DC Resistance Vramp_pp := SP7655 Internal RAMP Amplitude Peak to Peak Voltage Condition Cz2 >> Cp1 and R1 >> Rz3 Output Load Resistance >> Resr and Rdc Figure 11. Voltage Mode Control Loop with Loop Dynamic for Type III Compensation 5 The simple guidelines for positioning the poles and zeros and for calculating the component values for Type III compensation are as follows: a. b. c. d. e. f. g. h. i. Choose fco = fs / 5 Calculate fp_LC fp_LC = 1 / 2 [(L) (C)] ^ 1/2 Calculate fz_ESR fz_ESR = 1 / 2 (Resr) (Cout) Select R1 component value such that 50k R1 100k Calculate R2 base on the desired Vout R2 = R1 / [(Vout / 0.80V) - 1] Select the ratio of Rz2 / R1 gain for the desired gain bandwidth Rz2 = R1 (Vramp_pp / Vin_max) (fco / fp_LC) Calculate Cz2 by placing the zero at 1/2 of the output filter pole frequency Cz2 = 1 / (Rz2) (fp_LC) Calculate Cp1 by placing the first pole at ESR zero frequency Cp1 = 1 / 2 (Rz2) (fz_ESR) Calculate Rz3 by setting the second pole at 1/2 of the switching frequency and the second zero at the output filter double pole frequency Rz3 = 2 (R1) (fp_LC) / fs Calculate Cz3 from Rz3 component value above Cz3 = 1 / (Rz3) (fs) Choose 100pF Cf1 220pF to stabilize the SP7655ER internal Error Amplify j. k. 6 APPLICATION CIRCUIT FOR 12V INPUT Figure 12 shows another example of the SP7655ER configured for a common Bus Voltage conversion from +12V input to 3.3V output at 8A. U1 SP7655 1 PGND PGND PGND GND VFB COMP UVIN GND SS VIN VIN VIN VIN LX LX LX LX VCC GND GND GND BST NC LX LX LX 26 25 24 23 22 21 20 19 18 17 16 15 14 2 3 4 5 6 7 8 9 L1 IHLP-2525CZ-01-2R2MTR 2.2uH, Irate=8A DCR=10.4mOhm C3 47uF 6.3V CVCC 2.2uF DBST SD101AWS CBST 1uF CZ2 RZ2 2,200pF 7.68k,1% CP1 15pF CF1 100pF fs=300Khz RZ3 8.66k,1% CZ3 120pF VOUT 3.30V 0-8A R1 68.1k,1% GND2 C3 CERAMIC 1210 X5R R2 21.5k,1% CSS 47nF 10 11 12 VIN 12V C1,C4 CERAMIC 1210 Y5V C1 3.3uF 50V C4 3.3uF 50V 13 R3 200k,1% 1 2 3 U2 SPX5205 VIN GND EN BYP 4 VOUT 5 Notes: U1 Bottom-Side Layout should has three Contacts which are isolated from one of another, QT & QB Drain Contact and Controller GND Contact All resistor & capacitor size 0603 unless other wise specify GND R4 100k,1% C2 0.1uF Figure 12. SP7655ER configured for Vin = 12V, Vout = 3.3V at 0-8A Output Load Current Efficiency vs Load (12V to 3.3V) 100 E fficien cy % 90 80 70 60 0 1 2 3 4 5 6 7 8 Load Current (A) 3.340 3.335 3.330 3.325 3.320 3.315 3.310 3.305 3.300 0.5 1 2 3 4 5 6 7 8 Output Current (A) Output Voltage (Vdc) Load Regulation (12V to 3.3V) Figure 13. Efficiency vs Load Figure 14. Load Regulation Vout Vout Iout (2A/div) Iout (2A/div) Figure 15. Load Step Response: 5-8A Figure 16. Load Step Response: 0-6A 7 PC LAYOUT DRAWINGS Figure 17. SP7655EB Component Placement Figure 18. SP7655EB PC Layout Top Side Figure 19. SP7655EB PC Layout 2nd Layer Side 8 Figure 20. SP7655EB PC Layout 3rd Layer Side Figure 21. SP7655EB PC Layout Bottom Side 9 Table 1: SP7655EB List of Materials SP7655 Vin=28V Evaluation Board Rev. 00 List of Materials Line No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Ref. Des. PCB U1 U2 DBST D1 L1 C3 C1,C4 CVCC CBST C2 CSS CP1 CZ2 CF1 CZ3 RZ2 R2 RZ3 R1 R3 RBST R4 VIN, VOUT, GND, GND2 Qty. 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 4 Manuf. Sipex Sipex Sipex Vishay Semi ON Semi Vishay TDK TDK TDK Murata TDK Samsung AVX TDK ROHM AVX ROHM SEI Electronics Vishay Vishay Vishay ROHM Vishay Vector Electronic Manuf. Part Number F146-6570-00 SP7655EU SPX5205M5-5.0 SD101AWS MMSZ4678T1 IHLP-2525CZ-01-2R2MTR C3225X5R0J476M C3225X7R1H335M C1608X5R1A225K GRM188R61A105KA61D C1608X7R1H104K CL10B473KB8NNNC 06035A150JAT2A C1608COG1H222J MCH185A101JK 06035A121JAT2A MCR03EZPFX7681 RMC-1/16W-21.5K-1% CRCW0603-8661FRT1 CRCW0603-6812FRT1 CRCW0603-4993FRT1 MCR03EZPEFX20R0 CRCW0603-1003FRT1 K24C/M Layout Size 1.75"X2.75" DFN-26 SOT-23-5 SOD-323 SOD-123 6.86x6.47mm 1210 1210 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 0603 .042 Dia Component SP7655EB 2-FETs Buck Ctrl 150mA LDO Voltage Reg 15mA Schottky Diode 12V, 500mW Zener Diode 2.2uH Coil 8A 10.4mohm 47uF Ceramic X5R 6.3V 3.3uF Ceramic X7R 50V 2.2uF Ceramic X5R 10V 1.0uF Ceramic X5R 10V 0.1uF Ceramic X7R 50V 47,000pF Ceramic X7R 50V 15pF Ceramic COG 50V 2,200pF Ceramic COG 50V 100pF Ceramic COG 50V 120pF Ceramic COG 50V 7.68K Ohm Thick Film Res 1% 21.5K Ohm Thick Film Res 1% 8.66K Ohm Thick Film Res 1% 68.1K Ohm Thick Film Res 1% 499K Ohm Thick Film Res 1% 20.0 Ohm Thick Film Res 1% 100K Ohm Thick Film Res 1% Input/Output Terminal Posts 6/18/04 Vendor Phone Number 978-667-8700 978-667-8700 978-667-7800 402-563-6866 800-344-4539 914-347-2474 978-779-3111 978-779-3111 978-779-3111 978-779-3111 978-779-3111 978-779-3111 978-779-3111 978-779-3111 978-779-3111 978-779-3111 800-344-4539 800-344-4539 800-344-4539 800-344-4539 800-344-4539 800-344-4539 800-344-4539 800-344-4539 ORDERING INFORMATION Model Temperature Range Package Type SP7655EB...................................-40C to +85C..................SP7655 Evaluation Board SP7655ER.................................. -40C to +85C.......................................26-pin DFN 10 |
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