Specifications

dsPIC33F/PIC24H Family Reference Manual

43.11.5 PWM Pin Swapping

The SWAP PWMxH and PWMxL Pins bit, SWAP (IOCONx<1>), if set to ‘1’, enables the

user-assigned application to connect the PWMxH signal to the PWMxL pin and the PWMxL

signal to the PWMxH pin. If the SWAP bit (IOCONx<1>) is set to ‘0’, the PWM signals are

connected to their respective pins.

To perform the swapping function on the PWM cycle boundaries, the Output Override

Synchronization bit, OSYNC (IOCONx<0>), must be set. If the user-assigned application

changes the state of the SWAP bit (IOCONx<1>) when the module is operating and the OSYNC

bit (IOCONx<0>) is clear, the SWAP function attempts to execute in the middle of a PWM cycle

and the operation yields unpredictable results.

The SWAP function must be executed prior to the application of dead time. Dead time processing

is required since execution of switch function can enable the transistors in the user-assigned

application that are previously in disable state, possibly causing current shoot-through.

The SWAP feature is useful for the applications that support multiple switching topologies with a

single application circuit board. It also enables the user-assigned application to change the

transistor modulation scheme in response to changing conditions.

The SWAP function can be implemented by using either of the following methods:

• Dynamic Swapping: In the dynamic swapping, the state of the SWAP bit can be changed

dynamically based on the system response (for example, SMPS Power Control).

• Static Swapping: In static swapping, the SWAP bit is set during the start-up configuration

and remains unchanged during the program execution or on-the-fly (for example, Motor

Control).

43.11.5.1 EXAMPLE 1: PIN SWAPPING WITH SMPS POWER CONTROL

The SMPS Power Control example describes dynamic swapping. In power conversion

applications, the transistor modulation technique can be changed between the full-bridge Zero

Voltage Transition (ZVT) and standard full-bridge “on-the-fly” transition to meet different load and

efficiency requirements. The generic full-bridge converter as illustrated in Figure 43-43, can

operate in Push-Pull mode. The transistors are configured as follows:

•Q1 = Q4

•Q2 = Q3

The generic full-bridge converter can also operate in ZVT mode. The transistors are configured

as follows:

•Q1 = PWM1H

•Q2 = PWM1L

•Q3 = PWM2H

•Q4 = PWM2L

Figure 43-43: SMPS Power Control

OUT

+VIN