SP7656EB

SP7656 Evaluation Board Manual            Wide Input Voltage Range 5V – 29V 3 Amps Continuous 4 Amps Peak Output Current Internal Compensation Input Feedforward Control 600kHz Constant Frequency Operation Low 0.6V Reference Voltage High output setpoint accuracy of 1% Internal Soft Start Small SO8-EP Thermally Enhanced Package Adjustable Overcurrent Protection Lead Free, RoHS Compliant Package SP7656EB SCHEMATIC Rev 2/19/08 SP7656 Evaluation Manual Copyright 2007 Exar Corporation USING THE EVALUATION BOARD 1) Powering Up the SP7656EB Circuit Connect the Vin supply to the “VIN” and “GND” posts of SP7656 Evaluation Board with short leads. Connect a Load between the VOUT and GND posts, again using short leads to minimize parasitic inductance and voltage drop. 2) Measuring Output Load Characteristics It’s best to GND reference scope and digital meters using a single GND post in the output of the board. VOUT ripple can best be seen touching probe tip to the pad for C4 and scope GND collar touching Star GND post – avoid a GND lead on the scope which will increase noise pickup. 3) Using the Evaluation Board with Different Output Voltages While the SP7656 Evaluation Board has been tested and delivered with the output set to 3.3V, by simply changing one resistor, R2, the SP7656 can be set to other output voltages. The relationship in the Equation 1 is based on a voltage divider from the output to the feedback pin VFB, which is set to an internal reference voltage of 0.60V. Standard 1% metal film resistors of surface mount size 0603 are recommended. R2  R1 Vout (  1) 0.6V Equation 1 R1 resistance must remain 200kΩ for overall system loop stability. Note that since the SP7656 Evaluation Board design was optimized for 12V down conversion to 3.3V, changes of output voltage and/or input voltage will alter performance from the data given in the Power Supply Data section. POWER SUPPLY DATA The SP7656ER is designed with an accurate 2.0% reference over line, load and temperature. Figure 1 & 2 data show a typical SP7656 evaluation board efficiency and regulation plots, with efficiencies up to 87% and output currents up to 4A. The output voltage ripple of less than 6.6mV at full load and the LX node are shown in Figure 3. Figures 4 and 5 illustrate a 0.3A to 3A and 1.5A to 3A Load Step. Hiccup due to overcurrent is shown in Figure 6. Typical startup characteristics into a full load and no load are shown in Figure 7 and 8. All waveforms were taken under 12V to 3.3V conversion. While data on individual power supply boards may vary, the capability of the SP7656ER of achieving a high accuracy over a range of load conditions shown here is quite impressive and desirable for accurate power supply design. 2 E ffic ie n c y v s Io u t (3.3Vo u t) VF B v s Io u t (3.3Vo u t) 0.600 90 0.598 80 70 VF B (V) E ffic ien c y (%) 100 V in= 12V 60 V in= 24V 50 0.596 0.594 V in= 24V 0.592 40 0.0 1.0 2.0 3.0 V in= 12V 0.590 4.0 0.0 Io u t (A) 1.0 2.0 3.0 Io u t (A) Figure 1. Efficiency vs. Load Figure 2. VFB vs. Load Vout Transient SWN Output Ripple Iout: 1A/div ILx: 2A/div Figure 3. SWN & Output Ripple Voltage Figure 4. Load Step Response: 0.3A->3A Vout Transient Vout Iout: 1A/div Iout: 5A/div Figure 5. Load Step Response 1.5->3A Figure 6. Hiccup due to overcurrent Vin Vin Vout Vout Iout: 2A/div Iout: 2A/div Figure 7. Startup No Load Figure 8. Startup into 3A 3 4.0 PC Layout Drawings Figure 10. SP7656EB Top Side Component Placement Figure 11. SP7656EB Layout Top Side Figure 12. SP7656EB Layout Bottom Side 4 Table 1: SP7656EB Suggested Components and Vendor List Line No. 1 2 4 5 6 7 8 9 10 11 12 13 14 15 Ref. Des. PCB U1 D1 L1 D2 C1,C2 C1 C3.C4 C5,C7 C6 R1 R2 R3 R4 VIN, VOUT,GND, GND, SHDN Qty. Manuf. 1 1 1 1 1 21 2 2 1 1 1 1 1 Exar Exar On Semi WURTH MCC Taiyo Yuden MURATA MURATA MURATA VISHAY/DALE VISHAY/DALE VISHAY/DALE VISHAY/DALE 5 Vector Electronic Manuf. Layout Part Number Size 146-6651-01 1.175"x1.934" SP7656 SO-8 EP MBRA340T3 SMA 744314650 7.0X6.9mm 1N4148WX SOD323 UMK325BJ106MM-T 1210 GRM21BR60J226M 1210 GRM188R71H104K 0603 GRM1885C1H680J 0603 CRCW060320KFK 0603 CRCW060344K2FK 0603 CRCW06032K00FK 0603 CRCW06030000Z 0603 K24C/M .042 Dia Component SP7656EB Non-Sync. LED Driver Schotkky, 40V, 3A POWER-CHOKE WE-HC Fast Switching Diode 500mW 10uF Ceramic, 50V, X7S, 1210 22uF Ceramic X5R 6.3V 0.1uF Ceramic, X7R, 50V 68pF Ceramic, COG, 50V 200K Ohm 1%, 1/10W,0603 44.2k Ohm 1%, 1/10W, 0603 2.00K Ohm 1%, 1/10W, 0603 0.0 Ohm 1/10W, 5%, 0603 Vendor Phone Number 408-934-7500 408-934-7500 602-244-6600 201-785-8800 818-701-4933 800-388-2496 770-436-1300 770-436-1300 770-436-1300 402-563-6866 402-563-6866 402-563-6866 402-563-6866 Test Point Post 800-344-4539 ORDERING INFORMATION Model Temperature Range Package Type SP7656EB….............................-40C to +125C..............…...SP7656 Evaluation Board SP7656EN2-L.....................…. -40C to +125C........................………………….SO8-EP 5