MCF523X Datasheet, PDF (32/44 Pages) Freescale Semiconductor, Inc – DC Motor with Speed and Current Closed Loops, Driven by eTPU on

Software Design
For more details about the SC eTPU function, refer to Reference 7.
4.4.4 Current Controller (CC)
The current controller eTPU function is not intended to process input or output signals. Its purpose is to
control another eTPU function’s input parameter. The CC function can be executed even on an eTPU
channel not connected to an output pin. The CC function includes a general PID controller algorithm. The
controller calculates its output based on two inputs: a measured value, and a desired value. The measured
value (the actual DC-bus current) is usually provided by the analog sensing for DC motors (ASDC)
function, that preprocesses the measured analog values. The desired value is a CC function parameter, and
can be provided by the CPU or another eTPU function. In the motor-control eTPU function set, this
function mostly provides the current closed loop.
CC
applied voltage
PI controller
I_desired
I_actual
I_desired
Figure 21. Functionality of CC
For more details about the CC eTPU function, refer to Reference 9.
4.4.5 Analog Sensing for DC Motors (ASDC)
The analog sensing for DC motors eTPU function (ASDC) is useful for preprocessing analog values that
are measured by the AD converter and transferred to the eTPU data memory by DMA transfer. The ASDC
function is also useful for triggering the AD converter and synchronizing other eTPU functions.
All the above mentioned ASDC features are utilized in the application. The ASDC is initialized to run in
PWM synchronized mode, e.g. the first ASDC edge is synchronized with the beginning of the PWM
period. Simultaneously, the ASDC manages to synchronize the SC function (outer loop controller) by
generating the link to the SC channel every 16th ASDC period and to synchronize the CC function (inter
loop controller) by generating the link to the CC channel every ASDC period.
The ASDC function preprocesses the DC-bus current analog value and passes the adjusted value as an
input to the CC function. Processing of the DC-bus current analog value includes bit shifting and filtering.
DC Motor with Speed and Current Closed Loops, Driven by eTPU on MCF523x, Rev. 0
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