UM3501 EV Board User’s Guide UM3501 EV Board (Evaluation Kit) User’s Guide V1.0 Version Date 1.0 2012-05-11 http://www.union-ic.com Prvoider Approve Note Initial version. 1/10 UM3501 EV Board User’s Guide Table of Contents 1. Board Information 1.1 Schematic 1.2 PCB Layout 1.3 Interface Define 2. Board Operation 2.1 Power Supply 2.2 Enable 2.3 Output Setting 3. Board Component 3.1 Input Capacitor 3.2 Output Capacitor 3.3 Inductor 3.4 Sampling Resistor 4. PCB Layout Considerations http://www.union-ic.com 2/10 UM3501 EV Board User’s Guide 1 . Board Information This UM3501EVB uses a UM3501 adjustable output buck converter to step down 2.5-V or higher input voltages. The EVB operates over an input voltage range of 2.5V to 5.5V. The goal of the EVB is to demonstrate the small size of the UM3501 power supply solution and provide flexibility in interchanging the supporting passive components. This EVB include an enable jumper that allows the user to disable the device. 1.1 Schematic Fig 1.1 is UM3501 EVB design schematic. U1 VIN VIN 1 VIN SW 5 C1 4.7uF 2 GND VOUT L1 2.2uH R2 634k GND GND EN 3 EN FB R1 316k GND EN 1 2 3 C3 10uF 4 UM3501 VIN EN GND C2 option GND GND GND Fig 1.1 UM3501 EVB schematic （Recommended Value of R1 and R2 for 1.8V output） 1.2 PCB Layout http://www.union-ic.com 3/10 UM3501 EV Board User’s Guide Fig 1.2, Fig 1.3 is PCB layout and components location diagram of UM3501 EVB. Fig 1.2 UM3501 EV board PCB top layer Fig 1.3 UM3501 EV board PCB bottom layer http://www.union-ic.com 4/10 UM3501 EV Board User’s Guide 1.3 Interface Define Tab 1.1 is the directions of UM3501 EV board interface signals Tab 1.1 UM1661 EVB board interface Interface Function VIN Power supply input. GND Ground. EN VOUT Note 2.5V – 5.5V power supply. Chip enable/disable option. EN=ON (1): enable. EN=OFF (0): disable. The board output. UM3501 output. 2 . Board Operation An input power supply and a load must be connected to the appropriate EVB connectors in order for the EVB to operate. The absolute maximum input voltage is 6V. The UM3501 is designed to operate with a maximum input voltage of 5.5 V. Short pins 2−3 on jumper EN (labeled ON) to enable the device. Connect a load not to exceed 600 mA to the output of the EVB. Fig 2.1 shows the output ripple and switching waveform for UM3501’s operation. (VIN=3.6V, VOUT=1.8V, 300mA load current). http://www.union-ic.com 5/10 UM3501 EV Board User’s Guide SW VOUT Fig 2.1 UM3501 waveform diagram (VIN=3.6V, VOUT=1.8V, ILOAD=300mA) 2.1 Power Supply UM3501's input supply voltage range from 2.5V – 5.5V, you need to confirm there is sufficient margin with the current limit when use a DC source to supply the device. Input power cable should be thicker to reduce the loss of input voltage when the load current is large. 2.2 Enable EN jumper should be set to ON to enable the UM3501.EN jumper set to OFF to shut down the device. 2.3 Output Setting http://www.union-ic.com 6/10 UM3501 EV Board User’s Guide The output voltage of UM3501 is set by the external resistor divider. See Figure 1.1.The output voltage is calculated as VOUT=0.6V×(1+R2/R1) with R1+R2≤1MΩ. For stability, R1+R2 should not be greater than 1 MΩ. To keep the operating quiescent current to a minimum, the feedback resistor divider should have high impedance. For example: Use 634 k ohms R1 and 316 k ohms R2 to get a 1.8V output. VOUT=0.6V×(1+R2/R1)=0.6V×(1+634 /316)=1.80V 3. Board Component Tab 3.1 is the recommended BOM list of UM3501 EV board. Tab 3.1 UM3501 EV board recommended BOM list Reference U1 Union Buck Converter. C1 Capacitor,4.7uF,6.3V,Ceramic,X5R,0805. C2 Default for UM3501 Evaluation C3 Capacitor,10uF,6.3V,Ceramic,X5R,0805. L1 Inductor,2.2uH,850mA,33mΩ,SMT. R1,R2 3.1 Description Resistor, 1%,0603 or 0805 Part No. Manufacturer. UM3501 Union JMK212BJ475MG Taiyo - - C2012X5R0J106M TDK CDRH2D18/LD-2R2 Sumida Std Std Input Capacitor The input capacitors reduce the current peaks drawn from the battery or input power source and reduce switching noise in the IC. Ceramic capacitors with X5R or X7R temperature characteristics are highly recommended due to their small size, low ESR, and small temperature coefficients. A 4.7µF X5R or X7R capacitor (C1) from VIN to http://www.union-ic.com 7/10 UM3501 EV Board User’s Guide GND is recommended for most application. For optimum noise immunity and low input ripple, the input capacitor value can be increased. Note that some ceramic dielectrics exhibit large capacitance and ESR variation with temperature and DC bias. Ceramic capacitors with Z5U or Y5V temperature characteristics should be avoided. See Table 3.1 for suggested capacitors and manufacturers. 3.2 Output Capacitor The output capacitor limits the output ripple and maintains the output voltage during large load transitions. A 10μF X5R or X7R ceramic capacitor (C3) typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the ESR and ESL characteristics necessary for low output ripple. For optimum load-transient performance and very low output ripple, the output capacitor value can be increased; however, care should be taken with regards to output voltage slew rate requirements. Note that some ceramic dielectrics exhibit large capacitance and ESR variation with temperature and DC bias. Ceramic capacitors with Z5U or Y5V temperature characteristics should be avoided. Tantalum capacitors are not recommended. See Table 3.1 for suggested capacitors and manufacturers. 3.3 Inductor The step-down converter operates with a typical switching frequency of 1MHz. This operating frequency allows the use of physically small inductors while maintaining high efficiency. A 2.2µH to 4.7µH inductor is recommended for most applications. Inductor saturation current is another important parameter during inductor selection. http://www.union-ic.com 8/10 UM3501 EV Board User’s Guide Below formula shows how to calculate the actual peak inductor current under certain application. The saturation inductor current should be higher than the calculated value under the worse case. ΔIL =VOUT*(VIN-VOUT)/(VIN* L *fosc) IPEAK = ILOAD +ΔIL/2 Where ΔIL is Peak-Peak inductor ripple current, IPEAK is peak inductor current, ILOAD is maximum load current in the application. For example: 1.8V output at 3.6V input voltage, when choose a 2.2uH inductor, the value of the inductor Peak current at 600mA load current can be calculated as blow: ΔIL =VOUT*(VIN-VOUT)/(VIN* L *fosc)=1.8*(3.6-1.8)/(3.6*2.2*1)=0.409(A) IPEAK = IDC +ΔIL/2=0.6+0.409/2=0.805 (A) For optimum load transient and efficiency, low DCR inductors should be selected. See Table 3.1 for suggested inductors and manufacturers. 4. Layout Considerations For all switching power supplies, the layout is an important step in the design, especially at high-peak currents and switching frequencies. If the layout is not carefully done, the regulator shows stability problems as well as EMI problems. Good layout for the UM3501 can be implemented by following a few simple design rules. 1) Use wide and short traces for the high current paths. http://www.union-ic.com 9/10 UM3501 EV Board User’s Guide 2) The input capacitor, as well as the inductor and output capacitor, should be placed as close as possible to the IC pins. In particular, the input capacitor needs to be placed as close as possible to the IC pins, directly across the Vin and GND pin. 3) The feedback resistor network must be routed away from the inductor and switch node to minimize noise and magnetic interference. To further minimize noise from coupling into the feedback network and feedback pin, the ground plane or ground traces must be used for shielding. http://www.union-ic.com 10/10