Is Now Part of To learn more about ON Semiconductor, please visit our website at www.onsemi.com ON Semiconductor and the ON Semiconductor logo are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries. ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor s product/patent coverage may be accessed at www.onsemi.com/site/pdf/patent-marking.pdf. ON Semiconductor reserves the right to make changes without further notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information provided by ON Semiconductor. Typical parameters which may be provided in ON Semiconductor data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including Typicals must be validated for each customer application by customer s technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
www.fairchildsemi.com AN-1577 SG1577A Layout Guidelines Abstract This layout is important in high-frequency switching converter design. If designed improperly, PCB can radiate excessive noise and contribute to converter instability. Place the Pulse-Width Modulated (PWM) power stage components first. Mount all the power components and connections in the top layer with wide copper areas. The switchers of buck, inductor, and output capacitor should be as close to each other as possible to reduce the radiation of EMI due to the high-frequency current loop. If the output capacitors are placed in parallel to reduce the ESR of capacitor, equal sharing ripple current should be considered. Place the input capacitor near the drain of high-side MOSFET. In multi-layer PCB, use one layer as power ground and have a separate control signal ground as the reference for all signals. To avoid the signal ground being affected by noise and have best load regulation, it should be connected to the ground terminal of output. Checklists for Double-Layer PCB Follow the below guidelines for best performance: A double-layer printed circuit board is recommended. Use the bottom layer of the PCB as a ground plane and make all critical component ground connections through vias to this layer. Keep the traces running from the CLNx terminal to the output inductor be short. Use copper-filled polygons on the top (and bottom, if two-layer PCB) circuit layers for the CLNx node. The small-signal wiring traces from the DLx and DHx pins to the MOSFET gates should be kept short and wide enough to easily handle the several amps of drive current. The critical, small-signal components include any bypass capacitors (SMD-type of capacitors applied at VCC and SSx/ENB pins), feedback components (resistor divider), and compensation components (between INx and COMPx pins). Position those components close to their pins with a local, clear GND connection or directly to the ground plane. Keep those small-signal components and their wiring-traces far away the noisy generator of CLNx node. Place the bootstrap capacitor near the BSTx and CLNx pins. Place the ceramic capacitor (SMD or DIP type) near the VCC pin and GND pin to gain the noise immunity. The resistor on the RT pin should be near this pin and the GND return should be short and kept away from the noisy MOSFET GND (which is short together with IC s PGND pin to GND plane on back side of PCB). Place the compensation components close to the INx and COMPx pins. The feedback resistors for both regulators should be located as close as possible to the relevant INx pin with vias tied straight to the ground plane as required. Minimize the length of the connections between the input capacitors, CIN, and the power switchers (MOSFETs) by placing them nearby. Position both the ceramic and bulk input capacitors as close to the upper MOSFET drain terminal as possible and make the GND returns (from the source terminal of lower MOSFET to V IN capacitor GND) short. Position the output inductor and output capacitors between the upper MOSFET and lower MOSFET and the load. AGND should be on the clearer plane and kept away from the noisy MOSFET GND. PGND should be short, together with MOSFET GND, then through vias to GND plane on the bottom of PCB. The best high-current power loop as shown in Figure 1. Rev. 1.0.0 7/31/09
Snubber C IN C IN C IN (Ceramic) Lower Lower Upper Snubber C OUT C OUT C IN C IN C IN (Ceramic) Lower Lower Upper C OUT C OUT SG1577 Figure 1. Power Loop Practical Cases SG1577A is used for ATX power supply field, so SG1577A hosts the single-layer board or a daughter board plugged into the main board. The below sections provide good possible layouts for two cases. Case 1: Single-Layer Power Loop CLNx trace between high-side and low-side MOSFET should be copper-filled polygons. Do not use a jumper (which results in a parasitic inductance and induce a negative spike on this node). The specification for CLN to GND is: CLN to GND for 100ns Transient: -4V Min. 18V Max The high-current loop should be small to prevent EMI issues. The input capacitors (ceramic and E/C) and output capacitors should be near the relative rail. For a jumper used in the low-side MOSFET GND to V IN GND, consider the rating current. Two/three pieces of paralleled jumpers not only improved the rating current, but also reduced the parasitic inductance. Due to this jumper, the IC PGND should not be connected here! Rev. 1.0.0 7/31/09 2
Figure 2. Power Loop PGND & GND Use wiring-trace to connect PGND & GND. Do not use a jumper. If necessary, use 0Ω 0805/1206 resistors to be the jumpers. Figure 4. DHx & DLx Connection Small Signals The components related to this pin should be nearby. The critical pins are IN, COMP, BST, RT, SS/ENB, and VCC. If some of those components refer to ground, they should be tied to the GND pin (In this case, GND is the same as PGND). For any connection that can t use a jumper, 0Ω 0805/1206 resistors are recommended. The DIP-type of VCC capacitor can be closer to the VCC and GND pins for the best noise immunity. GND PGND Figure 3. PGND & AGND Wiring-trace Gate Connection Short and wide is hard to achieve in a one-layer board, do the best possible. Don t use the jumper to be the connector; 0Ω 0805/1206 resistors are recommended. Avoid passing through the CLNx node to avoid the noisy interference. Figure 4 also shows the position of SG1577A and power-mosfets relatively. Do not place SG1577A in the center of the power-mosfets even though this simplifies the trace wiring. PGND VCC V CC Cap. Figure 5. Small-Signal Components Placement Rev. 1.0.0 7/31/09 3
Case 2: Double-Layer of Daughter Board Power Loop Plan the flow of the power loop as smoothly as possible. The ceramic capacitors of VCC should be near the drain of upper MOSFET and the source of lower MOSFET. Use the copper planes in this loop as needed. Figure 6. Daughter Board (Top Layer) Figure 7. Main Board Power Loop Rev. 1.0.0 7/31/09 4
PGND & GND Use wiring trace to connect all of GND nets together, then tie PGND and GND on the GND plane. Figure 8. PGND & GND Wiring-Trace (Bottom Layer) Gate Connection Keep traces as short and wide as possible. Keep tracing on the bottom layer. Don t put tracing on the top layer near the noisy node. Don t use more than one via on DHx/DLx/CLNx traces to avoid the parasitic effect of the PCB. Small Signals The components related to this pin should be located near by. The critical pins are IN, COMP, BST, RT, SS/ENB, and VCC, as shown in Figure 9. Figure 9. DHx & DLx Connection (Bottom Layer) Rev. 1.0.0 7/31/09 5
Related Datasheets SG1577A- Dual Synchronous DC/DC Controller DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION, OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. Rev. 1.0.0 7/31/09 6
ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries. ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor s product/patent coverage may be accessed at www.onsemi.com/site/pdf/patent Marking.pdf. ON Semiconductor reserves the right to make changes without further notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information provided by ON Semiconductor. Typical parameters which may be provided in ON Semiconductor data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including Typicals must be validated for each customer application by customer s technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT: Literature Distribution Center for ON Semiconductor 19521 E. 32nd Pkwy, Aurora, Colorado 80011 USA Phone: 303 675 2175 or 800 344 3860 Toll Free USA/Canada Fax: 303 675 2176 or 800 344 3867 Toll Free USA/Canada Email: orderlit@onsemi.com Semiconductor Components Industries, LLC N. American Technical Support: 800 282 9855 Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: 421 33 790 2910 Japan Customer Focus Center Phone: 81 3 5817 1050 www.onsemi.com 1 ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative www.onsemi.com