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現在2147件がヒットしています。check
This is Sasaki in charge of power supply dock technology.
In this column, I would like to introduce some examples of problems related to power supplies that I encountered multiple times during various customer support sessions.
One day, I received an inquiry saying, ``My board is not working due to noise from the DC/DC converter, so I would like immediate support.''
What is the transmission path of switching noise?
Click here for detailed symptoms
- High-frequency switching noise is on the 0.9V line. ← High possibility of failure cause
- A board developed in the past with a similar combination (digital circuit & power supply) works fine
- Increasing the processing speed of digital ICs causes system errors
- The power supply capacity of the DC/DC converter is sufficient for the current consumption of the digital circuit.
Even though it satisfies the required specification of "core voltage 0.9V" recommended by IC manufacturers,
If you increase the processing speed of the digital circuit, the system will stop for some reason. . .
Schematics and layout diagrams are fine.
Could you show us the moment when the malfunction actually occurs?
Check for abnormal operation using the actual machine
There is no voltage drop on the 0.9V line, so there is no big problem. .
Is it possible that the switching noise of the power supply is the cause?
Is there no other way but to change to a low-noise DC/DC converter?
If that happens, it will be time consuming and costly. . .
As far as the waveform is concerned, it is hard to imagine that this power supply produces a particularly large amount of noise.
Could you show us the layout and layer structure of the entire board, not just the power supply part?
Check the layer structure of the entire board
I see, the 12V layer and the 0.9V layer overlap.
This seems to cause the switching noise on the 12V input line to couple into the 0.9V layer.
As a countermeasure, insert a GND between the 12V and 0.9V layers, or insert a bead filter in the DC/DC input section.
Yes, I will try!
As a result of implementing the above countermeasures, this problem was successfully resolved, and the problem was solved with minimal modification without changing the power supply IC.
Cause of digital circuit malfunction
Switching noise generated on the input side of the DC/DC converter
(Big problem with overlapping two layers)
The point of this time
When using a digital IC that requires low voltage and high current, it is necessary to design the power supply for the entire board in consideration of the effects of switching noise.