The author: Huang Gang, Sun Yiwen, member of “We Media” of Mr. Yibo Science and Technology High Speed Mr. Huang Gang, Sun Yiwen, a member of “We Media”, The dusk is hazy, the moonlight is overflowing with clouds, and the high-rise buildings rising from the ground look like towering giants in the moonlight. From a distance, there stands a tall and majestic building, which is close to the downtown area, but it is very quiet. With the dark down with Mr. High Speed’s new member of the mood of Thunder Leopard: their confidence full of simulation of the power supply, can not find the problem. It all started yesterday.
Because Lei Bao is in the learning stage, the teacher Chris arranged a simulation practice project for Lei Bao yesterday, the requirement is to simulate the power supply voltage drop. After Lei Bao got it, he looked at the requirement excitedly, and his mouth was slightly raised. Isn’t this the simulation of pressure drop that he has practiced many times before? Easy as pie, hehe. It’s a pity that Leopard was floating away and didn’t see the weird smile on Chris’s lips after he asked for it. It must not be that simple.
Although the thought of contempt, but action to pay attention to, Lei Bao got the file, immediately into the working state, carefully checked the PCB design file, not a little detail, after confirming the correct start simulation 0.8V, Duang quickly ah, Lei Bao ran out of the result:
Voltage drop result: PASS Current density: PASS
Good start, Thunder Leopard simulation second power supply 0.55V:
Voltage drop result: PASS Current density: PASS
Thunder Leopard grinned to sort out the data report and sent it to his master Chris by email. Chris asked: so soon? Saw an eye report, as expected this boy or omission ah. The master said: you put these two kinds of power synchronization simulation, and then organize a report to me.
This is different. Although the leopard is reluctant to do it, it did not expect the result is very different this time.
Both power supply voltage drops FAIL.
Hence the scene at the beginning of the article, when Thunder Leopard looks at the simulation data in a depressed mood. Unreconciled Leopard back and forth to tamper several times, but always analysis does not come out the reason. See this scene of the master feel his figure some lonely, patted the man and machine in one of the Thunder Leopard: Leopard ah, do not want to two power all PASS? Thunder Leopard looked up at the master: really can, master?
The master saw the longing in Leopard’s eyes: Leopard ah, the water here is too deep for you to grasp, or the master to come. Then master operated the mouse skillfully to open the current density of GND layer under the two simulation states and the voltage drop parameters in the Report: what is the difference between them? Leopard stared at the parameters circled by the master and the current density of the GND layer, and suddenly understood.
GND layer pressure drop comparison can be seen, a single power supply simulation and two power supply simulation together, GND layer pressure drop difference is very big, Thunder Leopard open PCB design a look, the original only a GND layer. The master continues to say: “so two power supply synchronous simulation of time, will share a reflux ground, so the reflux of the ground plane will appear crowded.” Compared with the current density, there is indeed such a change, which is due to my negligence.
In conclusion, it has been assumed that the voltage drop only focuses on the power layer and ignores the GND layer. Fortunately, the current is small. If the GND layer is small and the current is large, the simulation error of the separate current will be larger. Maybe the density has exceeded 100A/mm2 and the voltage drop is not qualified without knowing it, so the correct results can not be simulated and the modification and optimization suggestions can not be put forward to improve the single board power system. This will eventually lead to various problems in the actual work of the board level power supply.
