AN2517 Freescale Semiconductor / Motorola, AN2517 Datasheet - Page 6

• Manufacturer Part Number: AN2517
• Description: 3-Phase Sine Wave Generator with Dead-Time Correction TPU Function Set
• Manufacturer: Freescale Semiconductor / Motorola

AN2517/D
Detailed Function Description
3-Phase Sine Wave
Generator with
Dead-Time
Correction – Top
(3SinDt_top)
and 3-Phase Sine
Wave Generator with
Dead-Time
Correction – Bottom
(3SinDt_bottom)
6
3-Phase Sine Wave Generator with Dead-Time Correction TPU Function Set (3SinDt) MOTOROLA
The 3SinDt_top and 3SinDt_bottom TPU functions work together to generate
a 6-channel, 3-phase PWM signal, with dead-time between the top and bottom
channels. In order to charge the bootstrap transistors, the PWM signals start to
run 1.6ms after their initialization (at 20MHz TCR1 clock). The functions
generate signals corresponding to amplitude of 0 (50% duty-cycle) until the first
reload values are processed.
The CPU controls the PWM output by setting the TPU parameters. The Stator
Reference Voltage Vector Amplitude Ampl, the Stator Reference Voltage
Vector angle Theta (32-bit) and the angle increment dTheta (32-bit), can be
adjusted during run time. The PWM period T and the prescaler – the number
of PWM periods per reload of new values – are also read at each reload, so
these parameters can be changed during run time. Conversely, the dead-time
(DT) and the minimum pulse width (MPW) are not supposed to be changed
during run time. The phase currents currentA, currentB and currentC are read
by the TPU asynchronously to the PWM parameters reload. They are read in
the last part of the edge-time calculation to reflect the latest state of the phase
currents. The CPU notifies the TPU that the new reload values are prepared by
setting the LD_OK parameter. The TPU notifies the CPU that the reload values
have been read, and new values can be written, by clearing the LD_OK
parameter.
The TPU function rotates the Stator Reference Voltage Vector by dTheta angle
each period. So the TPU can drive the motor with constant amplitude and
constant speed independently of the CPU. The CPU can adjust the Ampl
parameter to change the Stator Reference Voltage Vector amplitude and the
dTheta parameter to change the rotation speed. The CPU can also set the
absolute value of Stator Reference Voltage Vector angle Theta. To notify the
TPU that the Theta parameter should be loaded instead of using the buffered
value, the CPU must set LD_OK = $8001 instead of $0001.
The following equations describe how the 3-phase sine wave PWM signal high-
times ht
calculated:
Theta
s
s
s
A
B
Freescale Semiconductor, Inc.
C
For More Information On This Product,
cos
cos
A
, ht
s
Theta
Theta
B
Theta
A
, ht
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C
s
B
and transition times t
dTheta
120
low-high
and t
high-low
of each channel are