User manual

PSMC Designer User’s Guide
DS40001671B-page 32  2012-2013 Microchip Technology Inc.
FIGURE 2-22: FIXED DUTY CYCLE COMPLEMENTARY OUTPUT
2.19.15 3PH: 3-Phase PWM
3-Phase PWM mode is selected by clicking on the 3PH tab as shown in Figure 2-23.
3-Phase PWM is a special mode that generates the waveform for 6-step 3-phase
systems such as those for driving brushless DC motors. These systems have three half
bridges requiring two drive outputs each for a total of six channels. This mode uses the
steering control bits to drive two of the six channels at a time: one half-bridge high side
drive and another half-bridge low side drive both on.
A diagram is presented in the top center of the control that indicates the power voltages
applied to the system in each phase. Phases are labeled U, V and W. The phase U half
bridge is driven by channels A (high side) and B (low side) as indicated to the right of
the phase labels. Phases V and W are labeled similarly. You can also select which side
of the half bridge receives the Pulse-Width Modulation: High side, low side, or both.
Modulation is selected by the two check boxes to the left of the diagram.
Clicking on a radio button at the top of the diagram will select that phase drive
configuration. For example, as shown in Figure 2-23, high side modulation is checked
and radio button 1 is selected, thereby driving phase U high with modulation, phase V
low with no modulation, and phase W floating. The channel connections to achieve this
configuration are shown on the right.