Specifications

Section 43. High-Speed PWM

High-Speed PWM

43.11.5.2 EXAMPLE 2: PIN SWAPPING WITH MOTOR CONTROL

The Motor Control example describes static swapping. Consider a generic motor control system,

that is capable of driving two different types of motors, such as DC motors and three-phase AC

induction motors.

Brushed DC motors typically use a full-bridge transistor configuration, as illustrated in

Figure 43-44. The Q1 and Q4 transistors are driven with similar waveforms, while the Q2 and Q3

transistors are driven with the complementary waveforms. This is also known as “driving the

diagonals”. Note that the Q5 and Q6 transistors are not used in a brushed DC motor.

The transistors are configured as follows:

•Q1 = PWM1H

•Q2 = PWM1L

•Q3 = PWM2L

•Q4 = PWM2H

Figure 43-44: Motor Contro

When compared to the DC motor, an AC induction motor uses all the transistors in the full-bridge

configuration. However, the significant difference is that the transistors are now driven as three

half-bridges where the upper transistors are driven by the PWMxH outputs and the lower

transistors are driven by PWMxL outputs.

The transistors are configured as follows:

•Q1 = PWM1H

•Q2 = PWM1L

• Q3 = PWM2H (note the difference with DC motors)

• Q4 = PWM2L (note the difference with DC motors)

•Q5 = PWM3H

•Q6 = PWM3L

Example 43-24 shows the PWM pin swapping.

Example 43-24: PWM Pin Swapping

Full-Bridge Converter

+VIN

/* PWM Pin Swapping feature */

IOCONxbits.SWAP = 1;

/* PWMxH output signal is connected to the PWMxL pin and vice versa */