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BD63731EFV Datasheet(Fiches technique) 12 Page - Rohm
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BD63731EFV Datasheet(HTML) 12 Page - Rohm
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• 15 • 001
Output ON Time
Current Decay Time
PWM Constant Current Control - continued
Current Decay Mode
PWM Constant Current Control can be optionally set the current decay mode in which the ratio of fast and slow decay.
The following diagrams show the state of each transistor and the regenerative current path during the current decay
for each decay mode.
Figure 3. Route of Regenerated Current during Current Decay
The merits of each decay mode are as follows:
4.1 SLOW DECAY
The output current ripple is small and this is favorable for keeping motor torque high because the voltage
between the motor coils is small and the regenerative current decreases slowly. However, an increase in the
output current due to deterioration of the current control in the lower current operation in HALF STEP,
QUARTER STEP, 1/8 STEP, 1/16 STEP, due to the influence of the motor reverse electromotive voltage
during high pulse rate driving in the mode, the current waveform is not able to follow the change in the current
limit and the distortion and motor vibration increases. Thus, this decay mode is suited to FULL STEP mode or
low-pulse-rate driven HALF STEP, QUARTER STEP, 1/8 STEP or 1/16 STEP modes.
4.2 FAST DECAY
Fast decay decreases the regeneration current much more quickly than slow decay, reducing distortion of the
output current waveform. However, fast decay yields a much larger output current ripple, which decreases
the overall average current running through the motor. This causes two problems: first, the motor torque
decreases (increasing the current limit value can help eliminate this problem, but the rated output current
must be taken into consideration); and second, the power loss within the motor increases and thereby
radiates more heat. If neither of these problems is of concern, then fast decay can be used for high-pulse rate
HALF STEP, QUARTER STEP, 1/8 STEP or 1/16 STEP drive.
Additionally, this IC allows for MIX DECAY mode/AUTO DECAY mode that can help to improve upon problems that
arise from using fast or slow decay.
4.3 MIX DECAY
During current decay Switching between SLOW DECAY and FAST DECAY can improve current control
without increasing the current ripple. In addition, the time ratio of SLOW DECAY and FAST DECAY can be
changed by the voltage input to the MTH pin, and it is possible to achieve optimal control state for any motor.
During MIX DECAY mode about chopping cycle, the first (t
) of which operates the IC in SLOW DECAY
mode, and the remainder (t
) of which operates in FAST DECAY mode. However, if the output current
does not reach the set current limit during the first (t
) decay period, the IC operates in fast decay mode
4.4 AUTO DECAY
Current control capability can still be improved without making the current ripple big by using SLOW DECAY
and switches only to FAST DECAY when required. Decay mode becomes FAST DECAY only when output
current reaches the set value while at minimum ON time.
MTH Pin Input Voltage [V]
Current Decay Mode
0 to 0.3
0.4 to 1.0
1.5 to 2.0
3.1 to 3.5
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