UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
887 of 1269
NXP Semiconductors
UM10503
Chapter 30: LPC43xx Motor Control PWM (MOTOCONPWM)
30.8 Functional description
30.8.1 Pulse-width modulation
Each channel of the MCPWM has two outputs, A and B, that can drive a pair of transistors
to switch a controlled point between two power rails. Most of the time the two outputs have
opposite polarity, but a dead-time feature can be enabled (on a per-channel basis) to
delay both signals’ transitions from “passive” to “active” state so that the transistors are
never both turned on simultaneously. In a more general view, the states of each output
pair can be thought of “high”, “low”, and “floating” or “up”, “down”, and “center-off”.
Each channel’s mapping from “active” and “passive” to “high” and “low” is programmable.
After Reset, the three A outputs are passive/low, and the B outputs are active/high.
The MCPWM can perform edge-aligned and center-aligned pulse-width modulation.
Remark:
In timer mode, the period of a channel’s modulated MCO outputs is determined
by its Limit register, and the pulse width at the start of the period is determined by its
Match register. If it suits your way of thinking, consider the Limit register to be the “Period
register” and the Match register to be the “Pulse Width register”.
Edge-aligned PWM without dead-time
In this mode the timer TC counts up from 0 to the value in the LIM register. As shown in
, the MCO state is “A passive” until the TC matches the Match register, at which
point it changes to “A active”. When the TC matches the Limit register, the MCO state
changes back to “A passive”, and the TC is reset and starts counting up again.
Center-aligned PWM without dead-time
In this mode the timer TC counts up from 0 to the value in the LIM register, then counts
back down to 0 and repeats. As shown in
, while the timer counts up, the MCO
state is “A passive” until the TC matches the Match register, at which point it changes to “A
active”. When the TC matches the Limit register it starts counting down. When the TC
matches the Match register on the way down, the MCO state changes back to “A passive”.
Fig 99. Edge-aligned PWM waveform without dead time, POLA = 0
MAT
MAT
LIM
LIM
0
POLA = 0
timer reset
timer reset
MCOA
MCOB
active
active
passive
passive
passive
passive
active
active