SLVSEE8B November 2019 – May 2021 DRV8899-Q1
During PWM current chopping, the H-bridge is enabled to drive through the motor winding until the PWM current chopping threshold is reached. This is shown in Figure 7-6, Item 1.
Once the chopping current threshold is reached, the H-bridge can operate in two different states, fast decay or slow decay. In fast decay mode, once the PWM chopping current level has been reached, the H-bridge reverses state to allow winding current to flow in a reverse direction. The opposite FETs are turned on; as the winding current approaches zero, the bridge is disabled to prevent any reverse current flow. Fast decay mode is shown in Figure 7-6, item 2. In slow decay mode, winding current is re-circulated by enabling both of the low-side FETs in the bridge. This is shown in Figure 7-6, Item 3.
The decay mode is selected by the DECAY register as shown in Table 7-7.
|DECAY||INCREASING STEPS||DECREASING STEPS|
|000b||Slow decay||Slow decay|
|001b||Slow decay||Mixed decay: 30% fast|
|010b||Slow decay||Mixed decay: 60% fast|
|011b||Slow decay||Fast decay|
|100b||Mixed decay: 30% fast||Mixed decay: 30% fast|
|101b||Mixed decay: 60% fast||Mixed decay: 60% fast|
|110b||Smart tune Dynamic Decay||Smart tune Dynamic Decay|
|111b (default)||Smart tune Ripple Control||Smart tune Ripple Control|
Figure 7-7 defines increasing and decreasing current. For the slow-mixed decay mode, the decay mode is set as slow during increasing current steps and mixed decay during decreasing current steps. In full step and noncircular 1/2-step operation, the decay mode corresponding to decreasing steps is always used.