MCF8316A: TSD bit

PS. 
The driver does not get hot at all. I can attach some pictures with heat camera if necessary. 

Marcel,

Are you using our MCF8316A EVM or your own custom board? TSD should get triggered only when the die temperature  exceeds 150°C. How much current is the device drawing from the power supply when the motor is stationary?

Regards,

Vishnu

Hi Vishnu, 

Thanks for the response.

This happens on a custom board.

The current that is drawing at 16.0V is rather low, sometimes it occurs while starting in open loop. I cannot imagine the die gets over 150°C with less then 100mA getting drawn.

How come the other error bits are not set? Could it be a solder issue, like too long too hot?

Marcel

Hi Vishnu, 

It runs at 16V, 1A for 5 minutes no problems, but when the load is increased, even for the slightest amount of time, the TSD bit is set and the motor is stopped. 

Looks more like an overcurrent error than a overtemperature?

Marcel

Hi Vishnu,

The state after the error has occured is 0x0E (MOTOR_FAULT), as read from the ALGORITHM_STATE register 

Any ideas on how to solve this?

Marcel

Hi Marcel, 

Thanks for the additional info - will review further and follow up soon

Best Regards, 
Andrew 

Marcel,

Looks like the IC is getting heated up due to high current when the motor is loaded. This could be a PCB layout problem. Did you follow the layout guidelines mentioned in the datasheet?  How many layers does you board have? What is the copper trace thickness in the board? You can use the MCF8316A EVM PCB design files (download link: https://www.ti.com/lit/zip/SLLR119) as a reference. 

Regards,

Vishnu

Hi Vishnu,

Thanks for your response. 

That might be the problem, nothing else has changed from the previous test board. 

But then why is OT not set? Also the buck converter keeps enabled. 

I'll take another look at the guidelines and update the PCB as required and do some more testing. Thanks!

Regards,

Marcel

Marcel,

Not sure what you mean by OT? You mentioned earlier that TSD bit is set. This bit  gets set when the die temperature exceeds 150°C. Buck cannot be disabled in MCF8316A. 

Regards,

Vishnu

Hi Vishnu,

I'm referring to this chapter from the datasheet:

7.3.22.10 Thermal Shutdown (TSD)

If the die temperature exceeds the thermal shutdown limit (TTSD), all the FETs are disabled, the charge pump is shut down, and the nFAULT pin is driven low. In addition, the DRIVER_FAULT, OT and TSD bit in the status register are set to 1b. Normal operation resumes (driver operation and the nFAULT pin is released) when the die temperature decreases below the hysteresis point of the thermal shutdown limit (TTSD - TTSD_HYS). The TSD bit stays latched high indicating that a thermal event occurred until a clear fault command is issued through the CLR_FLT bit. This protection feature cannot be disabled.

This is not what I am seeing, I only see the TSD bit getting set, until the clear all faults bit is set. Is this an error in the datasheet?

Thanks!

Marcel

Marcel,

You're right. OT bit should get triggered along with the TSD bit when there is overtemperature shutdown. OT is bit 25 in GATE_DRIVER_FAULT_STATUS Register. Can you make sure you are reading the correct bit?

Regards,

Vishnu

Hi Vishnu,

That is what I thought, but this bit stays 0. I've verified by reading the register "manually" (without using my custom application). Only the DRIVER FAULT bit and TSD bit are set. I could verify this even more by using a logic analyzer on the I2C lines, but I don't think that is going to show something else. 

Moreover I also don't see the it retrying after it has cooled down.

Don't get me wrong, I agree this is probably a PCB layout problem, and it has something to do with heat, but I am wondering why I don't see the expected behaviour at that issue.

Thanks!

Marcel