Microchip Technology DM164130-10 User Manual
PSMC Designer User’s Guide
DS40001671B-page 38
2012-2013 Microchip Technology Inc.
FIGURE 3-2:
FIXED OFF-TIME WITH FALLING EVENT DELAY
This method inverts the output so that the synchronous duty cycle becomes the
off-time, and the off-time after the duty cycle end becomes the on-time. Use
auto-shutdown to start and stop the application.
off-time, and the off-time after the duty cycle end becomes the on-time. Use
auto-shutdown to start and stop the application.
3.2
3-PHASE VARIABLE DUTY CYCLE
3-Phase applications such as power supplies, AC induction motors, and tri-color LED
lighting, require three PWMs with a fixed-phase offset from each other. These
applications also require a variance of the PWM duty cycle from 0 to 100%. The rising
event phase-delay alone cannot be used to offset the waveforms because the rising
event delay subtracts from the time available for the duty cycle. For example, if a period
has 100 microseconds and the rising event time is 30 microseconds then the falling
event time after the rising event can be no larger than 70 microseconds, which is a
maximum duty cycle of 70%.
Phase delay can be implemented without losing duty cycle range by selecting the rising
event sync output option. When that option is selected then the synchronous rising
event time defaults to zero. In other words, the rising event time is the master’s phase
delayed sync output and the master’s synchronous rising edge event occurs at the
master’s period event.
Now consider how this affects the three PSMCs generating the three PWMs in the
three phase waveform:
• The first PSMC is the master for the second PSMC
• The second PSMC is the slave of the first PSMC but is also the master to the third
lighting, require three PWMs with a fixed-phase offset from each other. These
applications also require a variance of the PWM duty cycle from 0 to 100%. The rising
event phase-delay alone cannot be used to offset the waveforms because the rising
event delay subtracts from the time available for the duty cycle. For example, if a period
has 100 microseconds and the rising event time is 30 microseconds then the falling
event time after the rising event can be no larger than 70 microseconds, which is a
maximum duty cycle of 70%.
Phase delay can be implemented without losing duty cycle range by selecting the rising
event sync output option. When that option is selected then the synchronous rising
event time defaults to zero. In other words, the rising event time is the master’s phase
delayed sync output and the master’s synchronous rising edge event occurs at the
master’s period event.
Now consider how this affects the three PSMCs generating the three PWMs in the
three phase waveform:
• The first PSMC is the master for the second PSMC
• The second PSMC is the slave of the first PSMC but is also the master to the third
PSMC
• The third PSMC is the slave of the second PSMC and master of none
Setup for the three PSMCs of a PIC16(L)F1786 is as follows:
Setup for the three PSMCs of a PIC16(L)F1786 is as follows:
- Select the PIC16(L)F1786 and PSMC1
- Click on the Sync function: Set rising event as the sync output
- Click on the Timer function: Set the sync source to Off
- Click on the Period Event function: Set the period event time to the desired
- Click on the Sync function: Set rising event as the sync output
- Click on the Timer function: Set the sync source to Off
- Click on the Period Event function: Set the period event time to the desired
value. Click on the upper input line to the output OR gate to make the
synchronous connection.
synchronous connection.
- Click on the Rising Event function: Set the rising event delay to the desired
phase offset. Click on the upper input line to the output OR gate to make the
synchronous connection.
synchronous connection.
- Click on the Falling Event function: Set the falling event duty cycle to the
desired value. Click on the upper input line to the output OR gate to make the
synchronous connection.
synchronous connection.
- Click on the Modulation function: Enable modulation and set the source to
CM4 SYNC