PWM pulse width (tminpulse)

[pratibhasurabhi]

Hi all,

With reference to MC9S12ZVM-Family RM, I have a question about the PWM pulse width. A note states " The minimum PWM pulse on & off time must be tminpulse."

I checked the tminpulse on/off time in GDU Electrical characteristics. It is 2us(min).

Now considering the PWM is of 20 KHz, does this mean that minimum and maximum PWM duty that can be output is 4% (2us on-time) and 96% (2us off-time i.e 48us on-time). 

Or is this note of tminpulse applicable in the 1.13.8.2.2 High Side Charge Pump , where they have mentioned - "In order to speed-up the high-side gate voltage level directly after commutation, the software should drive
the first PWM cycle with a duty cycle meeting an on-time of at least tminpulse for the low-side drivers and
then switch back to 100% again"

Thank you in advance.

[danielmartynek]

Hi,

The bootstrap capacitors must be charged before the HS drivers are switched on.
And the capacitors are being charged only when the LS drivers are active.

The t_minpulse is the time that is required to charge the bootstrap capacitor (it is the minimum LS ON time), it depends on many parameters of the circuit but mainly on the size of the capacitor and the resistor in series.

Regards,

Daniel

[pratibhasurabhi]

Dear Daniel,

Understood.

Thank you!