DRV8711: predriver fault, Gate- Signal not stable, it drops with time

Hello,

This thread was moved to private email conversation. I was the TI employee who helped in the thread you posted.

The main conclusion that was reach is that the drop in the A2SH and AOUT2 signal is the result of the MOSFET not enhancing properly and its RDSon increasing causing the voltage dip and OCP fault.

Have you seen this issue is more that one IC and board? 

Regards,

Pablo Armet

Hi, so I'll change the MOSFET, then it should be okay?

That is one thing to try. And has this issue been observed in every device?

The customer from the previous thread was able to fix some of the false OCP faults by replacing the MOSFETs.

Regards,

Pablo Armet

We have observed this error on several PCBAs, it only occurred after some time and interestingly it only affects the A2HS signal so far. The supply voltage is 48V and the MOSFETs used are Infineon BSC070N10NS3G (see excerpt from data sheet below).

We have carried out further measurements. Insight:
- Figure 1: If the B1HS signal is active first after an ENABLE, then there is no error.

- Figure 2: If A1HS is active first after an ENABLE, we see that A2HS weakens during the first pulses, but then recovers. No error:

- Figure 3: If A2HS is active after an ENABLE, then there is an error.

Hi win,

Thank you for the information.

Allow me a day to take a look at this information.

regards,

Pablo Armet

Hi win,

I'm going to try to replicate this in the lab with one of our evaluation boards. Can you share with me the register values. Can you also share the STATUS register to see what fault is being triggered. It looks like OCP due to the voltage dip on A2SH but I want confirmation.

In the meantime, I recommend trying the following:

Increase TDRIVE to 2us. In my previous testing, increasing TDRIVE helped prevent OCP faults.

Regards,

Pablo Armet

Hi Pablo

This error does not occur with every unit! This error did not occur on the EVAL board either. It seems to be an error that can only occur after some operating time.
Unfortunately, I cannot easily read out the type of error from the register. The DRV8711 is operated with the following settings:

DRV8711_CTRL E19
DRV8711_TORQUE 1B9
DRV8711_OFF 028
DRV8711_BLANK 032
DRV8711_DECAY 202
DRV8711_STALL 83C
DRV8711_DRIVE 0F0
DRV8711_STATUS 000

Anyway, I can't explain the behaviour of the A2HS signal, regardless of what the register settings are. The A2HS signal behaves differently depending on the position (angle) at which the ENBALE signal is given (see pictures).

Best regards

Rene

Hi,

Thank you for the extra information. I will take a look at the register setting. 

Regards,

Pablo Armet