Precautions for Current Circuit in PCB design

Pay attention to the following basic items for the current loop:

1. If you use strip, try to bold it.

If the Grounding Connection on the PCB is to be considered, the design should be as rough as possible. This is a good rule of thumb, but you must know that the minimum width of the ground wire is the valid width from this point to the end. Here the "end" refers to the farthest point from the power connection end.

2. Ground loop should be avoided

3. If the ground plane cannot be used, a star connection policy should be adopted (see figure 6)

In this way, the local current independently returns to the power connection end. Figure 6 shows that not all devices have their own circuits, and U1 and U2 share the same circuit. You can follow the following 4th and 5th rules.

4. Digital current should not flow through the simulator

When a digital device is switched, the digital current in the circuit is quite large, but it is only instantaneous.Caused by the effective inductance and impedance of the ground. The calculation formula is v.
=
LDI/dt, where V is the generated voltage, L is the inductance of the ground plane or ground strip, Di is the current change of the digital device, and DT is the duration. The calculation formula for the effect on the ground impedance is V =
Ri,
Among them, V is the generated voltage, r is the ground plane or ground line impedance, I is the current change caused by digital devices. The voltage changes on the ground plane or ground line of the simulator change the relationship between the signal and ground (that is, the ground voltage of the signal) in the signal chain ).

5. High-speed current should not flow through low-speed Devices

Similar to the above, the ground return signal of a high-speed circuit also changes the voltage of the ground plane. The calculation formula for this interference is the same as that above. It is used for the inductance of ground plane or ground strip, V =
LDI/dT; Impedance of ground plane or ground strip, V = ri
. Similar to digital current, when the ground plane or ground line of the high-speed circuit passes through the simulator, the voltage changes on the ground will change the relationship between the signal and ground in the signal chain.

Figure 4 Use manual cabling as the top layer of the circuit board designed in the circuit schematic diagram shown in Figure 3

Figure 5 the bottom layer of the circuit board designed in the circuit schematic diagram shown in Figure 3 using a manual cabling

Figure 6 if the ground plane cannot be used, the "star" wiring strategy can be used to process the current loop.

 

Figure 7 the ground planes separated by each element are sometimes more effective than the consecutive ground planes. Figure B) the ground wiring strategy is more ideal than figure)

6. No matter what technology is used, the grounding circuit must be designed as the minimum impedance and the capacity resistance.

7. If the ground plane is used, separating the open ground plane may improve or reduce the circuit performance. Therefore, exercise caution when using the ground plane.

Effective Method 7 for separate analog and digital ground planes

In Figure 7, the precision analog circuit is closer to the plug-in, but is isolated from the switch current of the Digital Network and power supply circuit. This is a very effective method for isolating the grounding circuit. We have also used this technology for cabling in Figure 4 and figure 5 discussed earlier.