Microchip Technology DM164130-10 User Manual
PSMC DESIGNER
USER’S GUIDE
2012-2013 Microchip Technology Inc.
DS40001671B-page 37
Chapter 3. PSMC Tips
The following sections provide useful tips for getting the most out of the PSMC
peripheral.
peripheral.
3.1
VARIABLE PERIOD WITH FIXED OFF-TIME
Some power supply designs use a fixed off-time and then vary the duty cycle by
asynchronous feedback to terminate drive time and also start a new period. The first
configuration that comes to mind is shown in
asynchronous feedback to terminate drive time and also start a new period. The first
configuration that comes to mind is shown in
and is setup as follows:
- Period event: Asynchronous feedback
- Rising event: Synchronous time set to desired fixed off-time
- Falling event: Asynchronous feedback – same source as period event
- Rising event: Synchronous time set to desired fixed off-time
- Falling event: Asynchronous feedback – same source as period event
FIGURE 3-1:
FIXED OFF-TIME WITH RISING EVENT DELAY
This will not work because the timing of the asynchronous event relative to the
psmc_clk may cause the rising event to be suppressed.
An alternate method, shown in
psmc_clk may cause the rising event to be suppressed.
An alternate method, shown in
with Falling Event Delay, uses a fixed falling
event delay, which avoids the timing issue is setup as follows:
- Period event: Asynchronous feedback
- Rising event: Synchronous time set to zero
- Falling event: Synchronous time set to desired fixed off-time
- Shutdown level: Low
- Output polarity: Inverted
- Rising event: Synchronous time set to zero
- Falling event: Synchronous time set to desired fixed off-time
- Shutdown level: Low
- Output polarity: Inverted