bd6709fs ROHM Co. Ltd., bd6709fs Datasheet - Page 29

• Manufacturer Part Number: bd6709fs
• Description: Dc Brushless Motor Drivers For Cooling Fans Speed Controllable Single-phase Full-wave Dc Brushless Fan Motor Drivers
• Manufacturer: ROHM Co. Ltd.

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A2
7) PWM soft switching ＜ BD6721FS 、 BD6722FS ＞
(H+)-(H-)
The soft switching section is set to the timing before and after the change of the hall signal. The length of the soft
switching section can be changed by adjusting the amplitude of the hall signal. The soft switching section becomes
long if the amplitude of the hall signal is reduced, and the gradient of the output current becomes smooth. However,
when a soft switching is applied too much, torque shortage might be caused. Therefore, set to the hall signal amplitude
about 100mVpp that the reversely electromotive voltage is suppressed appropriately.
The soft switching function operates in the DC input application and the pulse input application.
Adjust the hall bias resistance so that the hall signal amplitude become large when you do not want to use the soft
switching function.
When Hall Amplitude =
large
Fig.91 Relation between hall signal amplitude and output wave
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A2
(H+)-(H-)
When Hall Amplitude =
appropriate
29/40
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A2
(H+)-(H-)
When Hall Amplitude =
small
…
SOFT SWITCHING