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Part: MPC5746C (Power Architecture Z4, SDK: NXP MPC57xx platform SDK)
During thermal chamber testing at 115°C ambient, our MPC5746C-based board becomes completely unresponsive on boot — no UART console output at all, and this happens on every boot attempt at that temperature. The part appears to fully recover after cooling: reflashing/rebooting at room temperature restores normal operation with no persistent damage.
Interestingly, we can still successfully reprogram flash via PEMicro JTAG debug probe while the board is at 115°C — we've confirmed this by flashing a build with an incremented version string at temperature and reading back the new version after cooling down. So the debug-probe flash path works at 115°C; only the application boot path hangs/bad state.
From manual it states MCU can with hold upto 125°C.
Could you please help us to root cause the issue and how fix this issue.
Hello,
From manual it states MCU can with hold upto 125°C.
Yes, that is not an issue.
Could you please help us to root cause the issue and how fix this issue.
Since this is your custom board and issue disappear after cooling I suspect:
1. Clock startup issue (highest probability)
At 115°C:
- External crystal (FXOSC) startup time increases.
- Oscillator gain margin decreases.
- Load capacitors shift value with temperature.
- PCB leakage increases.
The debugger can still access the part because debug logic uses its own infrastructure and does not depend on the application reaching main().
FXOSC status bits
CMU clock-monitor faults
FIRC-only boot experiment
Run entirely from FIRC and disable external crystal temporarily
The fact that JTAG programming continues to work at 115°C is the strongest clue that the core infrastructure remains alive and the failure is occurring very early in the application boot path rather than in the flash array itself
best regards,
Peter