STM32 custom board hardware errors

[BKN636]

Hello everyone,

im currently working on a custom pcb which uses the STM32L031K6 and im having some troubles with it.

Ive attatched the schematic and some oscilloscope measurements.

Fault description:

-random signals and floating voltage levels on various I/O pins

-fault occurence ranges from minutes to hours

-3rd board revision, changed several periphal ICs, same error pattern

-errors seems to occur at random, even when the board is in idle (no h bridge switching)

Board I/O:

-rs232 via uart (MAX3250)

-12bit dac via i2c (MCP4725)

-16bit adc via spi (INA240+ ADS8864)

-3 digouts for h bridge control (no pwm, just steady state enable/disable)

-1 digout for current control ic (drv110), gives static enable signal (drv110 drives h-bridge low side switch via pwm)

-2 digouts for led

-1 internal 12bit adc

Supply:

-24V lab supply behind transformer

Debug probe:

-Segger J link edu mini via usb isolator

Things ive tried:

-closely observed 3v3 supply, seems clean, no overvoltage during start up or sudden shut downs, tried several different switching controllers on each board revision, all seemed fine to me

-tried several compilers, eclipse, keil & atollic, projection creation & µC initialisation via cubemx, created projects with "normal code" (which seems to run decent on some board revisions), and some with no functional code with setting all digouts to zero

-tried all combinations for digouts & alternate functions, pushpull, open drain, /w & w/o pullup/pulldowns

-replaced µC numerous times, all seem to get faulty after a while (perhaps faulty batch/damage during storage?)

-obviously the i/o ports seemed to get damaged, but why several at the same time?

Appreciate any help from you guys.

Kind regards

[JGerb]

or maybe both internal pullups are blown on, or something like that. Would be interesting to see if you can pull that voltage around or not. If it's quite stiff (try pullup/down with an external 10k e.g.) it might point to excessive current being drawn or perhaps its shorted to the micro's internal regulator output. Or a wierd power supply issue like one of the bond wires to 3V3 inside the chip being broken. Congrats on a fascinating problem.

[BKN636]

Yay me 😅

Perhaps a new fresh batch of µCs and a new clean board revision will help. If not im starting to question my mental sanity