S12 / MagniV MicrocontrollersのトピックRe: MCU Reset for no apparent reason

MCU Reset for no apparent reason

manishsangram — Sun, 09 Jul 2023 08:12:12 GMT

We are using the S12Z (MC9S12ZVM family) for a critical automotive application.

The power supply via VSup of the board is directly connected to the battery/alternator of the car, so the input voltage is battery voltage to alternator voltage viz 12V - 14.5V

The system uses an on board power supply via a transistor using the BCLTC.

The BLDC 3phase motor is running under varying load and a such drawing about 0.5Amps to 3Amps.

It has been tested to run under this load on a simulated environment using a 12V power supply for days and it works without any problems.

It has been put in a car and used for days and never shows any issue.

However, in a car, sometimes it just stops. This is not a software issue because the simulator is running the same software for hundreds of hours at a stretch.

We are focusing on the power side of things at this point to determine the root cause.

If the issue was caused due to drop in voltage, it should be more likely to occur on the simulator which is running on a power supply compared to a car which is running on a battery and an alternator. We also considered that may be the stiffness of the voltage in the car could be causing an over voltage due to a ripple though we have no evidence.

The following image from an oscilloscope when the system was running on the simulator shows the possible ripple that occurs on the power supply sometimes. The trigger is a 8ns pulse going below 10V when running on 12.5V fully charged automotive battery. This did NOT cause the reset, but it shows what happens momentarily.

The blue like shows the PWM pulse and the yellow line shows the input from the battery going to Vsup. We can see that when the MOSFET shut, it causes a ripple in the input which is really short, about 10ns peek to peek.

Can anyone indicate if such a tiny ripple has the potential to reset the MCU? Is this kind of a ripple acceptable or this this an anomaly, even though it is detected only sometimes.

Note that we DO have a filter circuit on each BLDC channel.

NOTE that even though the input shows the ripple, the 5V supply from the BCTLC is relatively less but similar time period as it follows the input. This can be seen below

Re: MCU Reset for no apparent reason

danielmartynek — Tue, 11 Jul 2023 07:33:52 GMT

Hi Manish,

Do you read the CPMURFLG register to identify the source of the reset?

The LVR monitors VDDF, VDD and VDDX.

Only the VDDX LVR assert level is specified:

Does the VDDX drop to ~3V?

Can you share the schematic?

If you don't want to share it here, please create a ticket,

Thanks,

BR, Daniel

Re: MCU Reset for no apparent reason

manishsangram — Tue, 11 Jul 2023 12:15:06 GMT

Hello Daniel,

We are aware of the CPMURFLG however this issue only occurs in the field when actually attached and working in an automobile and we have no way of retrieving this information.

I will see if we can share part of the schematic or create a ticket.

The VDDX falling below ~3V is unlikely, we have not encountered, however is there any time related information about how long VDDX needs to go below ~3V to reset the MCU? As you can see in my original post, there are ripples that last 5-9ns whose -peak might touch that, however we can't reproduce the reset in the lab so all our oscilloscope information is while the system continues to work stably.

Re: MCU Reset for no apparent reason

danielmartynek — Wed, 12 Jul 2023 14:16:15 GMT

Hi @manishsangram,

The reset signal is asserted as soon as the voltage reaches the assert level within the range below, and stays asserted as long as the voltage is below the deassert level. Not sure if the LVR circuit can filter such transient events. But there is some hysteresis which ensures that the signal is asserted until the deasert level is reached.

The VDDF, and VDD low-voltage reset levels are not specified, but voltage drop there also causes LVR.

Maybe the root cause is EMC.

Do you have filters at HD and VBS?

Best regards,

Daniel

Re: MCU Reset for no apparent reason

manishsangram — Thu, 13 Jul 2023 13:52:57 GMT

Hello @danielmartynek ,

We are not using charge pump, so there is no filter for CP either.

We do have the VBS RC filter but please note this in the context of the image shared by you, in our circuit R6 and C8 are supposed to be the RC filter.

So unlike your diagram, your Rhs and Rflt are combined in our case into R6. Does this have any impact on the RC performance? We kind of removed Rhs because it was same as Rflt.

Also from your diagram Cg, we don't have it.

Re: MCU Reset for no apparent reason

danielmartynek — Fri, 21 Jul 2023 12:45:04 GMT

Hi @manishsangram,

I'm sorry for the delay, the community was down for a few days.

1. Rhs and Rflt can be combined this way.

2. But regardless of the charge pump, the HD pin should be protected.

Regards,

Daniel

Re: MCU Reset for no apparent reason

manishsangram — Thu, 26 Dec 2024 16:05:05 GMT

Hi,

Despite our best efforts, the MCU is still blowing up sometimes. It is very difficult to figure out what is happening because it happens sometimes. Strangely most of the time re-flashing the chip starts it but not resetting the power. In rare cases the MCU dies. When the MCU dies, powering up the MCU we can feel the MCU is overheated which means something has blow internally.

Is there any application note specifically for the HD Pin protection or is there any guidance on how this has to be done correctly?

We are a bit vary to blindly add an RC filter to the HD pin because we are not sure if it is okay to add a resistor in series to HD pin etc.

Is there anything else to look into? This is very frustrating and now we are close to going into production so we need this resolved 100%

Re: MCU Reset for no apparent reason

manishsangram — Thu, 26 Dec 2024 16:25:35 GMT

Since we are not using BST and CP, for us the VSUP and HD are directly connected like this.

And on VSUP we have multiple capacitors (not RC filter) and TVS arranged like this

Re: MCU Reset for no apparent reason

manishsangram — Thu, 26 Dec 2024 17:06:12 GMT

@danielmartynek Request you to please look into this ASAP.

Re: MCU Reset for no apparent reason

danielmartynek — Mon, 30 Dec 2024 13:12:45 GMT

Hi @manishsangram,

I'm sorry for the delay, I'm out of office right now.

Refer to the attached document.

Slides 12 - 15.