Reason for masking 6 gate signals at startup|Hall sensor sample code

[pratibhasurabhi]

Hi All,

This is regarding the hall sensor sample code (MC9S12ZVML128_BLDC_Hall).

I will be attaching the code.

I have couple of questions about it.

Q1. From initPMF(), my understanding is that high and low side PWM are masked (PMFCGG2).

       Can you please tell me why all 6 PWM were masked.

      (I am asking this since, general instruction says the boostrap capacitors must be precharged before turning on the high-side drivers for the first time, and to do this, the low side driver must be switched on to charge the Cbs)

Q2. This question is to understand the mechanism behind the high side driving incase low side are not turned on to charge Cbs.

Update :

I have observed the LGx signals on DSO during the power up sequence. I am attaching them for reference.

I am also attaching a DSO snapshot where after some time from power up (i.e 5 seconds), motor starts running with the Hall sensor read value as 1

For Hall sensor 1, the output pattern for H bridge is U phase will have PWM, Wphase low side is on.

From the snap it is evident that Wphase low side[WL] first turns on and then Uphase high side PWM is applied

Question is : Is that time difference between WL rise and UH rise dead time? and how UH was able to drive if considering the low side are not turned on after power up.

Thank you in advance 

[danielmartynek]

Hi pratibhasurabhi,

I'm sorry for the delay.

There is indeed no code that would pre-charge the bootstrap capacitors before it starts running apart from the out-of-reset state of the LS drivers, which was discussed here: Regarding LGx signal behaviour 

If you want to be sure the capacitors are charged before the HS drivers are turned on, you can implement your own solution to that.

If the bootstrap capacitors were discharged and the first attempt to open the HS drivers failed, it should work for the second time anyway, because in the meantime the bootstrap capacitors get charged.

Also, if the charge pump is enabled, it can supply the HS drivers as well.

The delay is probably the dead time + t_delon / t_deloff.

Regards,

Daniel

[pratibhasurabhi]

Hi danielmartynek‌,

I understood.

I have one query related to - "If the bootstrap capacitors were discharged and the first attempt to open the HS drivers failed, it should work for the second time anyway, because in the meantime the bootstrap capacitors get charged".

My understanding is that if the first attempt to open HS driver is failed, that lead to detection of desaturation error of that particular high side.

Is this correct?

Please confirm

[danielmartynek]

Hi pratibhasurabhi,

Yes, that's correct.

After the t_blank time, when the charge pump connects to the driver, the particular HS driver is expected to be open from the Cb already.  

BR, Daniel