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MCT8314Z: MCT8314Z charge pump selection

wu shaohui
Prodigy 10 points
Part Number: MCT8314Z


Hi Team,

I have a question about this motor driver charge pump capacitor, the recommend capacitance is from 80nF to 330nF.

1. What are the principles for selecting capacitance values?

2. Now our selection of this capacitor is 22nF, the application is below 

   a. VM voltage is 9V 

   b. BLDC motor operation voltage is less than 100mA

3. The test charge pump voltage is VM+4.7V which tested with both 22nF and 11nF （50% lifetime drop）

What are your comments about 22nF use on our design? Is there any risk even its performance test is ok.

Thanks

Shaohui Wu

  • 0
    TI__Mastermind 38825 points

    您好

    已经收到了您的案例，调查需要些时间，感谢您的耐心等待

  • 0
    TI__Mastermind 38825 points

    Hi

    The charge pump range provided in the datasheet is worst case range. Typical value is 220nF and you may have typed wrongly as 22nF.

    This capacitor also should be twice voltage rated.

    This capacitor is used to charge the bulk capacitor (CP and VM node), number of time charging depends on the how fast bulk capacitor is discharging.

    You can make sure VCP voltage is within the limit under the operating conditions.

  • 0 回复 Daniel
    Prodigy 10 points

    Hello Daniel,

    Thanks for your quickly respond.

    Our test result VCP is 4.7VDC which one is within the limitation.

    There is another question that the datasheet recommends motor direction change when the motor is stationary.

    1. what is the risk if we change its direction during motor running?

    2.  If the direction of the motor is changed during operation but the voltage of the VVM does not increase at all, does this mean that there is no problem with this application?

    Thanks

    Shaohui Wu

  • 0 回复 wu shaohui
    TI__Mastermind 38825 points

    您好

    About new questions

    1. When motor is spinning and for dir change, we have to decelerate to safe speed without causing kinetic energy kickback, MCT8314Z is not closed loop speed controller, we need external MCU to control the speed and then change the direction.

    2. At low speed , some low inertia motor we may not see VM raise. But, do not recommend to change without stopping the motor.