AN2524 Freescale Semiconductor / Motorola, AN2524 Datasheet - Page 12

• Manufacturer Part Number: AN2524
• Description: DC Motor with Dead-Time Correction TPU Function Set
• Manufacturer: Freescale Semiconductor / Motorola

AN2524/D
Minimum Pulse Width
12
DC Motor with Dead-Time Correction TPU Function Set (DCmDt)
The TPU cannot generate PWM signals with duty cycle ratios very close to 0%
or 100%. This is the case when the dc value is close to 1 or –1. The minimum
pulse width that the TPU can be guaranteed to generate correctly is determined
by the TPU function itself and by the activity on the other channels. When the
TPU function is requested to generate a narrower pulse a collision can occur.
To prevent this, the parameter MPW (minimum pulse width) is introduced. The
TPU function DCmDt limits the narrowest generated pulse widths to MPW. The
CPU program should check the maximum absolute value of dc to prevent the
limitation, or take into account the non-linear performance when dc moves
towards the boundary values and the limitation is reached by the TPU. The
maximum absolute value of dc should satisfy:
The MPW is written by the CPU. The MPW depends on the whole TPU unit
configuration, especially the lengths of the longest states of the other functions,
and their prioroties, running on the same TPU and their priorities. The MPW
has to be correctly calculated at the time of the whole TPU unit configuration.
time slot
sequence
SW1
SW2
Freescale Semiconductor, Inc.
latency
For More Information On This Product,
Go to: www.freescale.com
Figure 6. Worst case timing – case one
DT
LH
LH
MPW
dc
C10
C10
1
( 2
DT
MPW
T
2
DT
)
MOTOROLA