Ringkasan dari tata letak desain dari DCDC switching daya pasokan
1. Handle the feedback loop (sesuai to R1-R2-R3-IC_FB&GND in the above figure). The feedback line should not go under the Schottky, the induktor (L1), the large kapasitor, or be surrounded by large current loops. , if necessary, a 100pF kapasitor can be added to the sampling resistor to increase stability (but the transient will be sedikit terpengaruh);
2. It is better to make the feedback line thin rather than thick, because the wider the line, the more obvious the antenna effect will be, which will affect the stability of the loop. generally use 6-12}mils wire;
3. Place all kapasitors as close to the IC as possible;
4. The induktor should be selected according to the capacity of 120-130% of the specifications. It should not be too large. If it is too large, it will affect the efficiency and transient state;
5. The capacitor is selected according to 150% of the capacity specified in the specification. If you are using chip ceramic capacitors, if you use 22uF, it would be better to use two 10uF in parallel. If cost is not sensitive, the capacitor can be larger. Special reminder: If the output capacitor is an aluminum electrolytic capacitor, remember to use a high-frequency and low-resistance capacitor. Do not just put a low-frequency filter capacitor!
6. Reduce the area surrounded by large current loops as much as possible. If it is not convenient to reduce it, use copper coating to make it a narrow slit.
7. Do not use thermal resistance pads on critical circuits, as they will introduce redundant inductance characteristics.
8. When using a ground layer, try to maintain the integrity of the ground layer beneath the input switching loop. Any cuts to the ground plane in this area will reduce the effectiveness of the ground plane, and even signal vias through the ground plane will increase its impedance.
9. Vias can be used to connect the decoupling capacitor and the ground of the IC to the ground layer, which can minimize the loop. But keep in mind that the inductance of a via hole is approximately 0.1~0.5nH, which varies depending on the thickness and length of the via hole, which can increase the total loop inductance. For low impedance connections, multiple vias should be used.
10. It should be noted that using the ground layer as a path for current return will introduce a lot of noise into the ground layer. For this reason, the local ground layer can be separated and then connected to the main ground through a point with very low noise.
11. When the ground layer is very close to the radiation loop, its shielding effect on the loop will be effective enhanced. Therefore, when designing a multi-layer PCB, the complete ground layer can be placed on the second layer, directly under the top layer that carries the high current.
12. Unshielded induktor akan menghasilkan a besar jumlah dari magnetik fluks kebocoran, yang akan masuk lainnya sirkuit dan filter komponen. Semi-terlindung atau sepenuhnya terlindung induktor harus menjadi digunakan dalam peka bising aplikasi, dan sensitif sirkuit dan loop harus menjadi disimpan menjauh dari induktor.
Troubleshooting EMI problems can be complex, especially when dealing with a complete system and not knowing where the sources of radiation are. With a basic knowledge of high frequency signals and current loops in switching converters, coupled with an understanding of how components and PCB layout behave at high frequencies, combined with the use of some simple homemade tools, it is possible to It is possible to easily solve EMI problems by identifying the sources of radiation and low-cost solutions to reduce emissions. The next issue of the trailer will bring you a DIY EMI detection tool. I believe that these experiences with switching power supplies will be of some help to some beginner engineers.
