SH7080_09 Datasheet, PDF (624/1622 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family

Section 11 Multi-Function Timer Pulse Unit 2 (MTU2)
10. Complementary PWM Mode PWM Output Generation Method
In complementary PWM mode, 3-phase output is performed of PWM waveforms with a non-
overlap time between the positive and negative phases. This non-overlap time is called the
dead time.
A PWM waveform is generated by output of the output level selected in the timer output
control register in the event of a compare-match between a counter and data register. While
TCNTS is counting, data register and temporary register values are simultaneously compared
to create consecutive PWM pulses from 0 to 100%. The relative timing of on and off compare-
match occurrence may vary, but the compare-match that turns off each phase takes precedence
to secure the dead time and ensure that the positive phase and negative phase on times do not
overlap. Figures 11.46 to 11.48 show examples of waveform generation in complementary
PWM mode.
The positive phase/negative phase off timing is generated by a compare-match with the solid-
line counter, and the on timing by a compare-match with the dotted-line counter operating with
a delay of the dead time behind the solid-line counter. In the T1 period, compare-match a that
turns off the negative phase has the highest priority, and compare-matches occurring prior to a
are ignored. In the T2 period, compare-match c that turns off the positive phase has the highest
priority, and compare-matches occurring prior to c are ignored.
In normal cases, compare-matches occur in the order a → b → c → d (or c → d → a' → b'),
as shown in figure 11.46.
If compare-matches deviate from the a → b → c → d order, since the time for which the
negative phase is off is less than twice the dead time, the figure shows the positive phase is not
being turned on. If compare-matches deviate from the c → d → a' → b' order, since the time
for which the positive phase is off is less than twice the dead time, the figure shows the
negative phase is not being turned on.
If compare-match c occurs first following compare-match a, as shown in figure 11.47,
compare-match b is ignored, and the negative phase is turned off by compare-match d. This is
because turning off of the positive phase has priority due to the occurrence of compare-match c
(positive phase off timing) before compare-match b (positive phase on timing) (consequently,
the waveform does not change since the positive phase goes from off to off).
Similarly, in the example in figure 11.48, compare-match a' with the new data in the
temporary register occurs before compare-match c, but other compare-matches occurring up to
c, which turns off the positive phase, are ignored. As a result, the negative phase is not turned
on.
Thus, in complementary PWM mode, compare-matches at turn-off timings take precedence,
and turn-on timing compare-matches that occur before a turn-off timing compare-match are
ignored.
Rev. 4.00 Dec. 15, 2009 Page 564 of 1558
REJ09B0181-0400