Products > Embedded Computing

How peaky is the Raspberry Pi4 current draw?

(1/3) > >>

e100:
How peaky is the 5v current draw for a Raspberry Pi4 with active WiFi and ethernet?

My Pi works fine with a Samsung 5v phone plug pack, however powering it from a cheap 5 amp buck converter gives sporadic low voltage warnings.
Apparently these are triggered if the supply dips under 4.65v, however I haven't been able to see anything out of the ordinary using a cheap battery powered oscilloscope. The lack of an AC coupled input makes it hard to see small dips on a 5v rail.

If these current spikes are only a few milliseconds then can I fix the issue by adding a cap on the input?

Whales:
Are you scoping the 5V on the raspi itself or at the output of your buck converter?  How long are the wires between each?  A few amps is a decent chunk of current, sub-par wires (including those in some USB cables) might be too resistive.

> using a cheap battery powered oscilloscope.

Does it have single-shot captures, or only does continuous triggering? 

e100:
Measuring at the Pi.
The scope only does continuous triggering.

I added a bunch of caps and that fixed the low voltage messages that previously appeared during boot up, however I still see an occasional message in dmesg.

RoGeorge:

--- Quote from: e100 on September 10, 2022, 06:53:13 am ---The lack of an AC coupled input makes it hard to see small dips on a 5v rail.

If these current spikes are only a few milliseconds then can I fix the issue by adding a cap on the input?

--- End quote ---

To make a DC coupled osciloscope AC coupled is easy, add a 100nF in series with the oscilloscope's probing tip, and probe through the capacitor.  You won't see the absolute DC value any more, but you'll see the variations from the average voltage, and you'll be able to use more sensitive ranges, like 0.1V/div or better.

There can be very, very short current spikes of a few amps (ns to ms long), very hard to visualize without writing dedicated test software loops, to make the power jumps repeatable for the oscilloscope. 


Try to add a 1000uF and a 100nF, both in parallel between GND and +5V, near the RPi.  Use short and thick copper wires.  Might give you less undervoltage alarms, but this is not a fix.  If the power supply is low quality or for lower current, no matter how much C you add, you might still get undervoltage, there's nothing you can do, except replacing the power supply with a proper one.

You may rather want to use the less powerful supply to charge the phone slower, and use the good Samsung charger for the RPi.


Instead of trying all these, better get a proper power supply of 5V and at least 3A, as per RPi4 specs.

SiliconWizard:
Yeah, the Pi4's current draw is peaky so it's pretty picky about power adapters. ^-^

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks WYSIWYG Editor
Powered by SMFPacks Advanced Attachments Uploader Mod