Motore di ricerca datesheet componenti elettronici |
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BD63621MUV Scheda tecnica(PDF) 9 Page - Rohm |
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BD63621MUV Scheda tecnica(HTML) 9 Page - Rohm |
9 / 29 page 9/24 BD63621MUV TSZ02201-0P2P0B701290-1-2 © 2017 ROHM Co., Ltd. All rights reserved. 21.Dec.2020 Rev.002 www.rohm.com TSZ22111・15・001 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 to 0.3 SLOW DECAY 0.4 to 1.0 MIX DECAY 1.5 to 3.5 FAST DECAY Figure 7. Relation between CR terminal voltage, MTH voltage, and output current during mixed decay CR Voltage Current limit value Output Current 0A GND 1.0V 0.4V SLOW DECAY FAST DECAY Chopping Period tchop MTH Voltage t1 t2 t3 |
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