BD63715AEFV_15 Datasheet, PDF (10/27 Pages) Rohm – 36VHigh-performance High-reliability Withstand Voltage Stepping Motor Driver

BD63715AEFV
Datasheet
○Current decay mode
The IC allows for a mixed decay mode in which the ratio of fast and slow decay can be optionally set.
The following diagrams show the operating state of each transistor and the regenerative current path during attenuation for
each decay mode:
FAST DECAY
SLOW DECAY
ON→OFF
OFF
ON→OFF
OFF→OFF
M
M
OFF→ON
ON→OFF
OFF→ON
ON→ON
Output ON Time
Current Decay Time
Figure 5 Route of Regenerated Current during Current Decay
The merits of each decay mode are as follows:
○SLOW DECAY
During current attenuation, the voltage between motor coils is small and the regeneration current decreases slowly,
decreasing the output current ripple. This is favorable for keeping motor torque high. However, due to fall-off of current
control characteristics in the low-current region, or due to reverse EMF of the output motors exhibited when using
high-pulse-rate half-step or quarter-step modes, the output current increases, distorting the output current waveform and
increasing motor vibration. Thus, this decay mode is most suited to full-step modes, or low-pulse-rate half-step or
quarter-step modes.
○FAST DECAY
Fast decay decreases the regeneration current much more quickly than slow decay, greatly 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- or quarter-step drive.
Additionally, this IC allows for a mixed decay mode that can help improve upon problems that arise from using fast or slow
decay alone. In this mode, the IC switches automatically between slow and fast decay, improving the current control
characteristics without increasing the output current ripple. The ratio of fast to slow decay is set externally via the voltage
input to the MTH pin; therefore, the optimal mix of slow and fast decay can be achieved for each application. Mixed decay
mode operates by splitting the decay period into two sections, the first X%(t1-t2) of which operates the IC in slow decay
mode, and the remainder(t2-t3) of which operates in fast decay mode. However, if the output current (i.e., the voltage on
the RNF pin) does not reach the set current limit during the first X% (t1-t2) decay period, the IC operates in fast decay
mode only.
MTH voltage [V]
Current decay mode
0~0.3
0.4~1.0
1.5~3.5
SLOW DECAY
MIX DECAY
FAST DECAY
t1
t2 t3
1.0V
CR Voltage
Output Current
Chopping Period
t_chop
MTH Voltage
0.4V
GND
Current limit value
SLOW FAST
DECAY DECAY
0A
Figure 6 Relation between CR terminal voltage, MTH voltage, and output current during mixed decay
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TSZ22111・15・001
10/23
TSZ02201-0P2P0B700440-1-2
16.Jun.2015 Rev.002