Special Consideration For Pwm Operation In Over-Modulation - Analog Devices ADSP-BF506F Hardware Reference Manual

Functional Description
Special Consideration for PWM Operation in
Over-Modulation
The Three-Phase PWM Timing Unit can produce PWM signals with
variable duty-cycle values at the PWM output pins. At the extremities of
the modulation process, both 0% and 100% modulation (termed
full off mode and full on mode, respectively) are possible. In between, for
other duty cycle values, the operation is termed normal modulation.
• Full On Mode. The PWM for any pair of PWM signals is said to
operate in full on mode when the desired high side output of the
Three-Phase PWM Timing Unit is in the "on" state (low or high as
specified by
successive
tue of the commanded duty cycle values (in conjunction with the
PWM_DT
• Full Off Mode. The PWM for any pair of PWM signals is said to
operate in full off mode when the desired high side output of the
Three-Phase PWM Timing Unit is in the "off" state (high or low as
specified by the
successive
the commanded duty cycle values (in conjunction with the
register).
• Normal Modulation. The PWM for any pair of PWM signals is
said to operate in normal modulation when the desired output duty
cycle is other than 0% or 100% between successive
pulses.
Certain situations exist whereby it is necessary to transition into or out of
full on mode or full off mode in order to insert additional "emergency
dead time" delays to prevent potential shoot-through conditions in the
inverter. Crossover usage also can potentially cause outputs to violate
shoot-through condition criteria, as described in
page 14-25. These transitions are detected automatically and, if
14-20
PWM_POLARITY
rising edges. This state may be entered by vir-
PWM_SYNC
register).
PWM_POLARITY
pulses. This state may be entered by virtue of
PWM_SYNC
ADSP-BF50x Blackfin Processor Hardware Reference
bit of the
PWM_CTRL
bit of the
PWM_CTRL
"Crossover Feature" on
register) between
register) between
PWM_DT
PWM_SYNC