Technical rules and application of regulated power supply PCB layout
Switching power supply PCB layout technical rules
The capacitance of the bypass ceramic capacitor should not be too large, and its parasitic series inductance should be minimized. Multiple capacitors connected in parallel can improve the high-frequency impedance characteristics of the capacitor
When the operating frequency of a capacitor is below fo, the capacitive impedance Zc decreases with the increase of frequency; when the operating frequency of the capacitor is above fo, the capacitive impedance Zc will become like the inductive impedance and increase with the increase of frequency; when the capacitor works When the frequency is close to fo, the impedance of the capacitor is equal to its equivalent series resistance (RESR).
Electrolytic capacitors generally have a large capacitance and a large equivalent series inductance. Because of its low resonant frequency, it can only be used for low frequency filtering. Tantalum capacitors generally have larger capacitance and smaller equivalent series inductance, so its resonant frequency will be higher than that of electrolytic capacitors, and can be used in medium and high frequency filtering. The capacitance and equivalent series inductance of ceramic chip capacitors are generally very small, so its resonance frequency is much higher than that of electrolytic capacitors and tantalum capacitors, so it can be used in high-frequency filtering and bypass circuits. Since the resonant frequency of small capacitance ceramic chip capacitors will be higher than that of large capacitance ceramic chip capacitors, so in
When selecting a bypass capacitor, ceramic chip capacitors with too high capacitance cannot be selected. In order to improve the high-frequency characteristics of capacitance, multiple capacitors with different characteristics can be connected in parallel to use the improved impedance effect after multiple capacitors with different characteristics are connected in parallel. It is not difficult to understand the importance of this typesetting rule through analysis. Shows the different ways of routing the input supply (VIN) to the load (RL) on one PCB. In order to reduce the ESL of the filter capacitor (C), the lead length of the capacitor pin should be kept as short as possible: while the traces of VIN positive to RL and VIN negative to RL should be as close as possible.
