Datasheet
PIC16(L)F1782/3
DS41579D-page 226 Preliminary 2011-2012 Microchip Technology Inc.
24.4 Dead-Band Control
The dead-band control provides non-overlapping
PWM signals to prevent shoot-through current in
series connected power switches. Dead-band control
is available only in modes with complementary drive
and when changing direction in the ECCP compatible
Full-Bridge modes.
The module contains independent 8-bit dead-band
counters for rising edge and falling edge dead-band
control.
24.4.1 DEAD-BAND TYPES
There are two separate dead-band generators
available, one for rising edge events and the other for
falling edge events.
24.4.1.1 Rising Edge Dead Band
Rising edge dead-band control is used to delay the
turn-on of the primary switch driver from when the
complementary switch driver is turned off.
Rising edge dead band is initiated with the rising edge
event.
Rising edge dead-band time is adjusted with the
PSMC Rising Edge Dead-Band Time (PSMCxDBR)
register (Register 24-25).
If the PSMCxDBR register value is changed when the
PSMC is enabled, the new value does not take effect
until the first period event after the PSMCxLD bit is set.
24.4.1.2 Falling Edge Dead Band
Falling edge dead-band control is used to delay the
turn-on of the complementary switch driver from when
the primary switch driver is turned off.
Falling edge dead band is initiated with the falling
edge event.
Falling edge dead-band time is adjusted with the
PSMC Falling Edge Dead-Band Time (PSMCxDBF)
register (Register 24-26).
If the PSMCxDBF register value is changed when the
PSMC is enabled, the new value does not take effect
until the first period event after the PSMCxLD bit is set.
24.4.2 DEAD-BAND ENABLE
When a mode is selected that may use dead-band
control, dead-band timing is enabled by setting one of
the enable bits in the PSMC Control (PSMCxCON)
register (Register 24-1).
Rising edge dead band is enabled with the PxDBRE
bit.
Rising edge dead band is enabled with the PxDBFE
bit.
Enable changes take effect immediately.
24.4.3 DEAD-BAND CLOCK SOURCE
The dead-band counters are incremented on every
rising edge of the psmc_clk signal.
24.4.4 DEAD-BAND UNCERTAINTY
When the rising and falling edge events that trigger the
dead-band counters come from asynchronous inputs,
there will be uncertainty in the actual dead-band time of
each cycle. The maximum uncertainty is equal to one
psmc_clk period. The one clock of uncertainty may still
be introduced, even when the dead-band count time is
cleared to zero.
24.4.5 DEAD-BAND OVERLAP
There are two cases of dead-band overlap and each is
treated differently due to system requirements.
24.4.5.1 Rising to Falling Overlap
In this case, the falling edge event occurs while the
rising edge dead-band counter is still counting. The
following sequence occurs:
1. Dead-band rising count is terminated.
2. Dead-band falling count is initiated.
3. Primary output is suppressed.
24.4.5.2 Falling to Rising Overlap
In this case, the rising edge event occurs while the
falling edge dead-band counter is still counting. The
following sequence occurs:
1. Dead-band falling count is terminated.
2. Dead-band rising count is initiated.
3. Complementary output is suppressed.
24.4.5.3 Rising Edge-to-Rising Edge or
Falling Edge-to-Falling Edge
In cases where one of the two dead-band counters is
set for a short period, or disabled all together, it is
possible to get rising-to-rising or falling-to-falling
overlap. When this is the case, the following sequence
occurs:
1. Dead-band count is terminated.
2. Dead-band count is restarted.
3. Output waveform control freezes in the present
state.
4. Restarted dead-band count completes.
5. Output control resumes normally.