UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
875 of 1269
NXP Semiconductors
UM10503
Chapter 30: LPC43xx Motor Control PWM (MOTOCONPWM)
If the channel’s CENTER bit is 0 but the DTE bit is 1, the match triggers the channel’s
deadtime counter to begin counting -- when the deadtime counter expires, the channel’s A
output switches from “passive” to “active” state.
30.7.5.2 Match register in Center-Aligned mode
If the channel’s CENTER bit in CON is 1 selecting center-aligned mode, a match between
TC and MAT while the TC is incrementing switches the channel’s B output from “active” to
“passive” state, and a match while the TC is decrementing switches the A output from
“active” to “passive”. If the channel’s CENTER bit in CON is 1 but the DTE bit is 0, a match
simultaneously switches the channel’s other output in the opposite direction.
If the channel’s CENTER and DTE bits are both 1, a match between TC and MAT triggers
the channel’s deadtime counter to begin counting -- when the deadtime counter expires,
the channel’s B output switches from “passive” to “active” if the TC was counting up at the
time of the match, and the channel’s A output switches from “passive” to “active” if the TC
was counting down at the time of the match.
30.7.5.3 0 and 100% duty cycle
To lock a channel’s MCO outputs at the state “B active, A passive”, write its Match register
with a higher value than you write to its Limit register. The match never occurs.
To lock a channel’s MCO outputs at the opposite state, “A active, B passive”, simply write
0 to its Match register.
30.7.6 MCPWM Dead-time register
This register holds the dead-time values for the three channels. If a channel’s DTE bit in
CON is 1 to enable its dead-time counter, the counter counts down from this value
whenever one its channel’s outputs changes from “active” to “passive” state. When the
dead-time counter reaches 0, the channel changes its other output from “passive” to
“active” state.
The motivation for the dead-time feature is that power transistors, like those driven by the
A and B outputs in a motor-control application, take longer to fully turn off than they take to
start to turn on. If the A and B transistors are ever turned on at the same time, a wasteful
and damaging current will flow between the power rails through the transistors. In such
applications, the dead-time register should be programmed with the number of PCLK
periods that is greater than or equal to the transistors’ maximum turn-off time minus their
minimum turn-on time.
[1]
If ACMODE is 1 selecting AC-mode, this field controls the dead time for all three channels.
[2]
If ACMODE is 0.
Table 708. MCPWM Dead-time register (DT - address 0x400A 003C) bit description
Bit
Symbol
Description
Reset value
9:0
DT0
Dead time for channel 0.
0x3FF
19:10
DT1
Dead time for channel 1.
0x3FF
29:20
DT2
Dead time for channel 2.
0x3FF
31:30
-
reserved