Going to STOP mode during low voltage

[razvanb]

Hello,

I have recently  came upon a strange problem while using the S12ZVL64 MCU:

While going to sleep mode from an under voltage situation the MCU will never wake up if the voltage returns to normal values.

This issue only happens on one project that has a bigger capacitor on the supply line(220uA), other parts work fine with the same code.

The way I reproduce it is to simply switch off the power supply. If I switch on the power supply until the capacitor is not empty the MCU never wakes up.

The code uses the low voltage interrupt to trigger the transition to STOP mode. I dont think the code is to blame because other parts with smaller capacitor work fine with same code, seems more like a timing issue inside the MCU

Do you have any hint for me ? I checked the errata but no mention of this.

Best Regards,

Razvan

[razvanb]

Hi,

I solved this a while back but in case somebody has the same problem the issue was the priority of the low voltage interrupt, it was higher then the SCI interrupt and it was blocking the wake-up.

Best Regards,

Razvan

[razvanb]

Hello,

The STOP instructions is called in interrupt context but before STOP the CAN transceiver is set to wakeable S-bit is cleared, Interrupts are enabled by clearing the I bit and the next instruction is STOP.

Yes, LVR level is not reached, I dont have the exact Voltage value but it was between 5V - 4V. 

The MCU does not reset, I can see this on the oscilloscope..the voltage not as steep as soon as the MCU will go to sleep. If I connect the power supply after the voltage drops below 3V the MCU will behave normally.

Best Regards,

Razvan

[danielmartynek]

Hi,

I don't understand this sentence: "If I connect the power supply after the voltage drops below 3V the MCU will behave normally", because if VDDX < 3V, the MCU must reset.

Could you use a voltage regulator to set VSUP and VDDX between LVI (4.04V) and LVR (3.13V) precisely?

Regards,

Daniel 

[danielmartynek]

Hi,

Where did you place the STOP instruction, in the ISR?

So the VDDX voltage never reach LVR assert level (typ. 3.02V) and the MCU does not reset.

Is that correct? 

Thanks,

Daniel