SLOSE70 December 2020 DRV8434S
PRODUCTION DATA
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, as soon as the PWM chopping current level is reached, the H-bridge reverses state by switching on the opposite arm MOSFETs to allow the winding current to flow in the opposite direction. As the winding current approaches zero, the H-bridge is disabled to prevent further reverse current flow. Fast decay mode is shown in Figure 7-6, item 2. In slow decay mode, the winding current is re-circulated by enabling both low-side MOSFETs in the H-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.