Texas Instruments Evaluation Module for the DRV8829 DRV8829EVM DRV8829EVM Datenbogen
Produktcode
DRV8829EVM
Quadrant 1
Quadrant 2
Quadrant 3
Quadrant 4
Ix Increases
Ix Increases
Ix Decreases
Ix Decreases
Phase
Decay
UART Mode
As a result, we will want to use slow decay during most of the time, with the exception being those periods
of the microstepping cycle in which waveform generation is compromised. This translates to the usage of
slow decay mode while the winding current is charging (Quadrants 1 and 3 as seen in
of the microstepping cycle in which waveform generation is compromised. This translates to the usage of
slow decay mode while the winding current is charging (Quadrants 1 and 3 as seen in
) and fast
decay mode during while the winding current is discharging (Quadrants 2 and 4 as seen in
The microcontroller firmware is in charge of modulating the Decay pin HI or LO depending on sine wave
quadrant generation. The decay information is stored inside the same lookup table which holds the sine
wave magnitude and phase information.
quadrant generation. The decay information is stored inside the same lookup table which holds the sine
wave magnitude and phase information.
Figure 9. Decay Mode
Another option is to use mixed decay mode. Because mixed decay mode is a current decay rate which is
in between fast and slow, it uses the best of both scenarios and gives us a reasonable current regulation
rate (low current ripple and good enough average current) while allowing us to discharge the winding and
preserve sine wave shape.
in between fast and slow, it uses the best of both scenarios and gives us a reasonable current regulation
rate (low current ripple and good enough average current) while allowing us to discharge the winding and
preserve sine wave shape.
When using mixed decay mode, there is no need to switch between slow and mixed or mixed and fast
during sine wave generation, although each application is unique and exploring these options is
recommended.
during sine wave generation, although each application is unique and exploring these options is
recommended.
The decay mode frame allows the user to select between the slow/fast decay mode or mixed decay mode
of sine wave generation. Only one option can be selected at any given time. Selection can be done prior
to motor enablement or during normal motor run time.
of sine wave generation. Only one option can be selected at any given time. Selection can be done prior
to motor enablement or during normal motor run time.
4.4.4
Microstepping Resolution
Segmenting a full step into microsteps can be achieved by how many times we can divide the current
regulation magnitude. Because the VREF input on the DRV8828 or DRV8829 devices is an analog input,
we could in essence generate an infinite amount of microsteps. Our analog voltage generator, however, is
not an infinitesimally divisible analog function and can only give us up to 4096 different voltage outputs,
which is more than plenty to generate any useful amount of microsteps.
regulation magnitude. Because the VREF input on the DRV8828 or DRV8829 devices is an analog input,
we could in essence generate an infinite amount of microsteps. Our analog voltage generator, however, is
not an infinitesimally divisible analog function and can only give us up to 4096 different voltage outputs,
which is more than plenty to generate any useful amount of microsteps.
12
DRV882x Evaluation Modules
SLMU002
–
June 2011
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©
2011, Texas Instruments Incorporated