SP7650 Evaluation Board Manual Easy Evaluation for the SP7650ER 12V Input, 0 to 3A Output Synchronous Buck Converter Built in Low Rds(on) Power FETs UVLO Detects Both VCC and VIN High Integrated Design, Minimal Components High Efficiency: 90% Feature Rich: UVIN, Programmable Softstart, External VCC Supply and Output Dead Short Circuit Shutdown SP7650EB SCHEMATIC U1 SP7650 L1 1 26 PGND LX VOUT 6.8uH 2 25 PGND LX 3.30V CZ2 RZ2 RZ3 3 24 PGND LX 0-3A C3 7.15k,1% 1,000pF 15k,1% 4 23 GND LX R1 22uF CP1 5 22 6.3V CZ3 68.1k,1% VFB VCC 150pF 22pF 6 21 COMP GND CVCC 7 20 fs=300Khz 2.2uF CF1 UVIN GND 8 19 GND2 100pF DBST GND GND RBST 9 18 C3 R2 SS BST 20 21.5k,1% 10 17 CERAMIC CSS SD101AWS VIN NC 1210 47nF 11 16 VIN LX X5R CBST 12 15 12V VIN LX 6,800pF 13 14 VIN LX VIN R3 R6 C1 200k,1% Notes: CERAMIC C1 U1 Bottom-Side Layout should has 1210 464,5% 22uF three Contacts which are 1210 X5R D1 16V isolated from one of another, QT BZX384B5V6 R4 & QB Drain Contact and C2 Vz=5.6V 100k,1% GND 0.1uF Controller GND Contact All resistor & capacitor size 0603 unless other wise specify Date: 01/04/05 SP7650 Evaluation BoardManual Copyright 2005 Sipex Corporation USING THE EVALUATION BOARD 1) Powering Up the SP7650EB Circuit Connect the SP7650 Evaluation Board with an external +12V 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 Its best to GND reference scope and digital meters using the Star GND post in the center of the board. VOUT ripple can best be seen touching probe tip to the pad for C3 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 SP7650 Evaluation Board has been tested and delivered with the output set to 3.30V, by simply changing one resistor, R2, the SP7650 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 SP7650 Evaluation Board design was optimized for 12V 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 SP7650ER provides short circuit protection by sensing Vout at GND. POWER SUPPLY DATA The SP7650ER is designed with a very accurate 1.0% reference over line, load and temperature. Figure 1 data shows a typical SP7650 Evaluation Board Efficiency plot, with efficiencies to 90% and output currents to 3A. SP7650ER Load Regulation is shown in Figure 2 of only 0.1% change in output voltage from no load to 3A load. Figures 3 and 4 illustrate a 1.5A to 3A and 0A to 3A 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 SP7650ER 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 40mV at no load to 3A load. While data on individual power supply boards may vary, the capability of the SP7650ER of achieving high accuracy over a range of load conditions shown here is quite impressive and desirable for accurate power supply design. 2