2020-09-17 06:11 PM
I have a Nucleo H745ZI-Q board powered from the CN1 STLINK USB port. I am observing bursts of noise on the 5V line.
The noise is 150mV p-p, burst of about 6 (80us) pulses, every 18ms.
The H745 is idle and the debugger is not active.
I have tried several different USB ports and adapters all with the same noise on the 5V.
Has anybody seen this? What could be causing the current draw?
2020-09-18 09:24 AM
What do you mean by "idle"? Is NRST pulled low?
It could also be something upstream of the USB connector. Does it still happen if you use a power supply?
2020-09-21 09:52 AM
The NRST line is high (not held in reset). By "idle" I mean the H745 MCU is not running a program (either core).
I have tried different USB power supplies, resulting in the same noise observations above. Later this week I will try a bench 5Vdc supply.
Thanks
2021-04-15 08:47 AM
It is the Ethernet PHY, it is active even without any MAC running in the MCU. To disable it, you need to remove SB177 and tie the concave pad to ground.
2021-04-15 09:04 AM
Tight while(1) loops are not fuel efficient