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

Question asked by PRATIBHA SURABHI on Jul 2, 2020
Latest reply on Jul 17, 2020 by Daniel Martynek

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 

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