BLDC acceleration problem

[moha-affa]

hi ...
im using 18f2431 ... the program from AN899 .. everything seems to be ok

but the the motor doesn't always start , sometimes it starts and sometimes doesn't and sometimes starts with weared voice and high temperature ....
the hall sensors are good on oscilloscope they give six combination ...

i couldnt see the problem :(

can anyone help please ??

[Ttelmah]

Are you pre-charging the high side FET's?.

Most circuits (all those using charge pumps to generate the power for the high side FET's), _require_ you to pre-charge these circuits before actually trying to start the motor. Typically something like 0.25 to 0.5 seconds. Depends on how your high side drive is done, but this is exactly the symptom this gives. It'll start OK 'sometimes'.

[moha-affa]

can you explain please ??? im kind of noobie in electronics

[moha-affa]

there is something else i forgot to say sorry ...

when the motor success to start im trying so start it again from the same position of the rotator and it always ok but from othor positions the problem comes ...