National Semiconductor Application Note 2074 Yang Zhang August 16, 2010 Introduction Evaluation Board Design Concept The LMZ1050xEXT SIMPLE SWITCHER® power module is a complete, easy-to-use DC-DC solution capable of driving up to 3A, 4A, or 5A load with exceptional power conversion efficiency, output voltage accuracy, line and load regulation. The LMZ1050xEXT is available in an innovative package that enhances thermal performance and allows for hand or machine soldering. The LMZ1050xEXT can accept an input voltage rail between 2.95V and 5.5V and deliver an adjustable and highly accurate output voltage as low as 0.8V. One megahertz fixed frequency PWM switching provides a predictable EMI characteristic. Two external compensation components can be adjusted to set the fastest response time, while allowing the option to use ceramic and/or electrolytic output capacitors. Externally programmable soft-start capacitor facilitates controlled startup. The LMZ1050xEXT is a reliable and robust solution with the following features: lossless cycle-by-cycle peak current limit to protect for over current or short-circuit fault, thermal shutdown, input under-voltage lock-out, and pre-biased startup. The evaluation board is designed to demonstrate low conducted noise on the input and output lines, as seen in Figure 11 and Figure 14. Four input capacitors (Cin1 - C in4) and three output capacitors (Co1 - Co3) are populated for this purpose. All the input and output filter capacitors are not necessary to comply with radiation standards. For a circuit example that passes radiated emissions standards (EN55022, class B) please refer to Figure 19. Additionally, Cin5 is present to reduce the resonance of the input line produced by the inductance and resistance in the cables connecting the bench power supply to the evaluation board and the input capacitors. Board Specifications • • • • • • • • VIN = 2.95V to 5.5V VOUT = 2.5V (default output voltage setting, refer to Table 2 for other output settings) ±2.5% feedback voltage accuracy at 2.5V output (Including line and load regulation from TJ = -55°C to 125°C) ±1.63% feedback voltage accuracy over temperature IOUT = 0A to 3A, 4A, and 5A θJA = 20°C/W, θJC = 1.9°C/W Designed on four layers, the top and bottom layers are 1oz. copper and the two inner layers are 1/2 oz. copper weight Measures 2.25 in. x 2.25 in. (5.8 cm x 5.8 cm) and is 62mil (.062”) thick on a FR4 laminate Additional Component Footprints LMZ1050xEXT Evaluation Board LMZ1050xEXT Evaluation Board When the tracking feature of the LMZ1050xEXT is used, remove the soft-start capacitor CSS and use a resistor divider on designators Rtrkb and Rtrkt. The ground and Vtrk post have been provided for easy connection. The LMZ1050xEXT eval board incorporates a precision enable circuit which is pulled high by a 100 kΩ pull up resistor to VIN. This allows the user to pull low on the enable pin to ground. The top enable resistor is Rent and the bottom enable resistor is Renb. Refer to the Design Guideline and Operating Description section of the LMZ1050xEXT data sheet for detailed design implementation. Select FPGAs specify input inrush currents for particular power-up sequences and others require sequencing rails to avoid start-up or latch-up problems. To prevent early turn-on of the LMZ1050xEXT in systems with multiple power rails, precision enable and tracking are useful as the main input voltage rail rises at power-up. AN-2074 © 2010 National Semiconductor Corporation 301280 www.national.com AN-2074 Component Circuit Schematic 30128017 FIGURE 1. Component Schematic for Evaluation Board TABLE 1. Bill of Materials for Evaluation Board, VIN = 3.3V to 5V, VOUT = 2.5V Designator Description Case Size Manufacturer Manufacturer P/N Quantity U1 SIMPLE SWITCHER® TO-PMOD-7 National Semiconductor LMZ10503/4/5EXTTZ 1 Cin1 1 µF, X7R, 16V 0805 TDK C2012X7R1C105K 1 Cin2, CO1 4.7 µF, X5R, 6.3V 0805 TDK C2012X5R0J475K 2 Cin3, CO2 22 µF, X5R, 16V 1210 TDK C3225X5R1C226M 2 Cin4 47 µF, X5R, 6.3V 1210 TDK C3225X5R0J476M 1 CO3 100 µF, X5R, 6.3V 1812 TDK C4532X5R0J107M 1 Rfbt 75 kΩ 0805 Vishay Dale CRCW080575K0FKEA 1 34.8 kΩ 0805 Vishay Dale CRCW080534K8FKEA 1 Rcomp 1.1 kΩ 0805 Vishay Dale CRCW08051K10FKEA 1 Ccomp 180 pF, ±5%, C0G, 50V 0603 TDK C1608C0G1H181J 1 Ren1 100 kΩ 0805 Vishay Dale CRCW0805100KFKEA 1 CSS 10 nF, ±5%, C0G, 50V 0805 TDK C2012C0G1H103J 1 Rfbb TABLE 2. Output Voltage Setting (Rfbt = 75 kΩ) www.national.com VOUT Rfbb 3.3 V 23.7 kΩ 2.5 V 34.8 kΩ 1.8 V 59 kΩ 1.5 V 84.5 kΩ 1.2 V 150 kΩ 0.9 V 590 kΩ 2 AN-2074 Complete Circuit Schematic 30128024 FIGURE 2. Complete Evaluation Board Schematic 3 www.national.com AN-2074 Connection Diagram 30128015 FIGURE 3. Efficiency Measurement Setup 30128016 FIGURE 4. Output Voltage Ripple Measurement Setup Efficiency vs. Load Current LMZ10504EXT & LMZ10505EXT, VOUT = 2.5V, TAMB = 25°C Efficiency vs. Load Current LMZ10503EXT, VOUT = 2.5V, TAMB = 25°C 30128028 www.national.com 30128031 4 AN-2074 Performance Characteristics 30128029 30128030 FIGURE 5. Current Derating vs. Ambient Temperature LMZ10503EXT, VIN = 5.0V, θJA = 20°C/W FIGURE 8. Current Derating vs. Ambient Temperature LMZ10503EXT, VIN = 3.3V, θJA = 20°C/W 30128022 30128023 FIGURE 6. Current Derating vs. Ambient Temperature LMZ10504EXT, VIN = 5.0V, θJA = 20°C/W FIGURE 9. Current Derating vs. Ambient Temperature LMZ10504EXT, VIN = 3.3V, θJA = 20°C/W 30128032 30128033 FIGURE 7. Current Derating vs. Ambient Temperature LMZ10505EXT, VIN = 5.0V, θJA = 20°C/W FIGURE 10. Current Derating vs. Ambient Temperature LMZ10505EXT, VIN = 3.3V, θJA = 20°C/W 5 www.national.com AN-2074 30128018 30128020 FIGURE 11. Output Voltage Ripple VIN = 5V, VOUT = 2.5V, IOUT = 3A, 4A, & 5A LMZ10503EXT / LMZ10504EXT / LMZ10505EXT FIGURE 14. Output Voltage Ripple VIN = 3.3V, VOUT = 2.5V, IOUT = 3A, 4A, & 5A LMZ10503EXT / LMZ10504EXT / LMZ10505EXT 30128037 30128036 FIGURE 12. Load Transient Response VIN = 5.0V, VOUT = 2.5V LMZ10503EXT, IOUT = 400 mA to 2.7A, 20 MHz Bandwidth Limit FIGURE 15. Load Transient Response VIN = 3.3V, VOUT = 2.5V LMZ10503EXT, IOUT = 300 mA to 2.7A, 20 MHz Bandwidth Limit 30128019 30128021 FIGURE 13. Load Transient Response VIN = 5V, VOUT = 2.5V LMZ10504EXT, IOUT = 400 mA to 3.6A, 20 MHz Bandwidth Limit www.national.com FIGURE 16. Load Transient Response VIN = 3.3V, VOUT = 2.5V LMZ10504EXT, IOUT = 400 mA to 3.6A, 20 MHz Bandwidth Limit 6 AN-2074 30128034 30128035 FIGURE 18. Load Transient Response VIN = 3.3V, VOUT = 2.5V LMZ10505EXT, IOUT = 500 mA to 4.5A, 20 MHz Bandwidth Limit FIGURE 17. Load Transient Response VIN = 5.0V, VOUT = 2.5V LMZ10505EXT, IOUT = 500 mA to 4.5A, 20 MHz Bandwidth Limit 7 www.national.com AN-2074 Circuit Example: Complies with EN55022 Class B Radiated Emissions 30128025 FIGURE 19. Component Schematic, VIN = 5V, VOUT = 2.5V, Complies with EN55022 Class B Radiated Emissions TABLE 3. Bill of Materials Designator Description Case Size Manufacturer Manufacturer P/N Quantity U1 SIMPLE SWITCHER® TO-PMOD-7 National Semiconductor LMZ10503/4/5EXTTZ 1 Cin1 1 µF, X7R, 16V 0805 TDK C2012X7R1C105K 1 Cin2 4.7 µF, X5R, 6.3V 0805 TDK C2012X5R0J475K 1 Cin3 47 µF, X5R, 6.3V 1210 TDK C3225X5R0J476M 1 CO1 100 µF, X5R, 6.3V 1812 TDK C4532X5R0J107M 1 Rfbt 75 kΩ 0805 Vishay Dale CRCW080575K0FKEA 1 Rfbb 34.8 kΩ 0805 Vishay Dale CRCW080534K8FKEA 1 Rcomp 1.1 kΩ 0805 Vishay Dale CRCW08051K10FKEA 1 Ccomp 180 pF, ±5%, C0G, 50V 0603 TDK C1608C0G1H181J 1 CSS 10 nF, ±5%, C0G, 50V 0805 TDK C2012C0G1H103J 1 30128038 30128026 FIGURE 20. Radiated Emissions (EN55022, Class B) VIN = 5V, VOUT = 2.5V, IOUT = 3A Tested on LMZ10503EXT Evaluation Board www.national.com FIGURE 21. Radiated Emissions (EN55022, Class B) VIN = 5V, VOUT = 2.5V, IOUT = 4A Tested on LMZ10504EXT Evaluation Board 8 AN-2074 30128027 FIGURE 22. Radiated Emissions (EN55022, Class B) VIN = 5V, VOUT = 2.5V, IOUT = 5A Tested on LMZ10505EXT Evaluation Board 9 www.national.com AN-2074 PCB Layout Diagram 30128007 FIGURE 23. Top Layer 30128008 FIGURE 24. Internal Layer I (Ground) www.national.com 10 AN-2074 30128011 FIGURE 25. Internal Layer II (Ground) 30128013 FIGURE 26. 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