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• the channel (n) is in EPWM mode,
• T is one unit of FTM counter,
• the EPWM duty cycle without edge dithering is [(C(n)V - CNTIN) x T],
• the number of PWM periods which duty cycle that has edge dithering is FRACVAL,
• the EWM duty cycle with edge dithering is [(C(n)V - CNTIN + 1) x T],
thus, the average duty cycle (in decimal) is [(C(n)V - CNTIN) + (FRACVAL/32)] x T,
where the integer value is (C(n)V - CNTIN) and the fractional value is (FRACVAL/32).
See the example below.
0x16 0x1B 0x00 0x05 0x0A 0x0F 0x14 0x19 0x1E 0x03 0x08 0x0D 0x12 0x17 0x1C 0x01 0x06 0x0B 0x10 0x15 0x1A 0x1F 0x04 0x09 0x0E 0x13 0x18 0x1D 0x02 0x07 0x0C 0x11 0x16 0x1B 0x00 0x05
EPWM duty cycle DC1 =
(C(n)V - CNTIN) x T
EPWM duty cycle DC2 =
(C(n)V - CNTIN + 1) x T
DC1
one unit of FTM counter
accumulator
overflow
32 x PWM periods
DC2
DC2
DC2
DC2
DC2
6 x DC1
6 x DC1
5 x DC1
5 x DC1
5 x DC1
PWM edge
dithering
channel (n) output
channel (n) output
channel (n) is in EPWM with high-true pulses
CNTIN = 0x0000
MOD = 0x0063
PS[2:0] = 3'b000
channel (n) ELSB:ELSA = 2'b10
C(n)V = 0x0032
channel (n) FRACVAL = 0x05
T is the period of one unit of FTM counter
Thus, the values (in decimal) are:
DC1 = 50 x T
DC2 = 51 x T
average duty cycle = (50 + 5/32) x T = 50.15625 x T
PWM edge
dithering
PWM edge
dithering
PWM edge
dithering
PWM edge
dithering
PWM edge
dithering
Figure 39-108. Example of Average Duty Cyle when the Channel (n) is in EPWM Mode
with PWM Edge Dithering
39.5.33.2.2 CPWM Mode
The PWM edge dithering for channel (n) in CPWM mode is enabled when a non-zero
value is written to the channel (n) FRACVAL.
If the channel (n) is in CPWM mode and the PWM edge dithering is enabled, at the end
of each CPWM period, the channel (n) FRACVAL value is added to the channel (n)
internal 5-bit accumulator. When this accumulator overflows (that is, the result of the
adding is greater or equal than 0x20), the accumulator remains with the rest of the
subtraction: (the result of this adding - 0x20).
In this configuration, if there was not the overflow of the channel (n) accumulator in the
current CPWM period, then the duty cycle is not modified by the PWM edge dithering,
that is, the initial edge of CPWM duty cycle happens on channel (n) match (FTM counter
= C(n)V) when the FTM counter is decrementing, and the final edge of CPWM duty
cycle on channel (n) match when the FTM counter is incrementing.
Functional description
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
998
NXP Semiconductors
Содержание Kinetis KE1xZ256
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