DRV8846_15 Datasheet, PDF (20/35 Pages) Texas Instruments – DRV8846 Dual H-Bridge Stepper Motor Driver

DRV8846
SLLSEK2 – JUNE 2014
www.ti.com
When the minimum drive time (t_BLANK) provides more current than the regulation point, fast decay of 1- t_BLANK is
applied. If the second drive period also provides more current than the regulation point, fast decay of 2 t_BLANK is
applied. If a third (or more) consecutive period provides more current than the regulation point, fast decay using
25% of t_OFF time is applied. When the minimum drive time is insufficient to reach the current regulation level,
slow decay is applied until the current exceeds the current reference level (see Figure 11).
Iref
tBLANK
tBLANK
tOFF (fixed)
tBLAN^tBKLANK
tBLANK
tOFF (fixed)
tBLANK ^{toff 25%}
FET Drive On (FWD or REV)
Slow Decay
Fast Decay
tOFF (fixed)
tBLANK
tOFF (fixed)
Figure 11. Adaptive Decay – Mixed Decay Operation
Figure 12 shows a case for adaptive decay where a step occurs. The system starts with 1 t_BLANK of fast decay
and works up to 25% of t_OFF time for fast decay until the current is regulated again.
Iref
tBLANK
tBLANK
tOFF (fixed)
tBLANK
tBLANK
tOFF (fixed)
tBLANK ^tBLANK
tOFF (fixed)
tBLAN^tKBLANK
FET Drive On (FWD or REV)
Slow Decay
Fast Decay
STEP
tBLANK
tOFF (fixed)
tBLANK^{toff 25%}
tBLANK^{toff 25%}
tBLANK^{toff 25%}
tBLANK
Figure 12. Adaptive Decay – Step Operation
8.3.5 Blanking Time
After the current is enabled in an H-bridge, the voltage on the xISEN pin is ignored for a period of time before
enabling the current sense circuitry. Note that the blanking time also sets the minimum drive time of the PWM.
The time, t_BLANK, is determined by the sine DAC code and the torque DAC setting. The timing information for
t_BLANK is given in Table 8.
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