• State Resolved
  • Locked Locked
  • Replies 9 replies
  • Subscribers 28 subscribers
  • Views 1008 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8818: capacitor

K.Hamamoto
Guru 12155 points
Part Number: DRV8818

HiI

read the following post. However I have some question about a capacitor for connecting to the pin.

https://e2e.ti.com/support/applications/motor_drivers/f/38/t/641646?tisearch=e2e-sitesearch&keymatch=DRV8818

1. Are there any recommended value range for CP1-CP2 and VCP and VGD?

   Our customer would like to consist that capacitor by a few (0.1uFx 2~3) parallel capacitor. (0.2~0.3uF is possible?) How much Is the range possible?

   (Please let me know if there is any other concerns.)

2. If those capacitor is too small or too large, what is affected to the operation?

3. How much is the maximum voltage will biased at CP1-CP2 and VCP and VGD pin?

   Our customer would like to consider the maximum biased voltage for the capacitor at those pins.

I saw the EVM BOM. The capacitor are used 50V capacitor. (C0805C224K5RACTU)

Should we use the 50V capacitor same as EVM? Or is it possible to use a capacitor less than 50V? (Supply Voltage : 24V +/-10%)

Best Regards,

Koji Hamamoto

  • 0
    TI__Guru** 114905 points
    Hi Hamamoto-san,

    1. Are there any recommended value range for CP1-CP2 and VCP and VGD?
    Typically +/- 50% is acceptable. Adding 2-3 0.1uF capacitors in parallel should be OK.

    2. If those capacitor is too small or too large, what is affected to the operation?
    This should be OK.


    3. How much is the maximum voltage will biased at CP1-CP2 and VCP and VGD pin?
    The EVM was designed for operation to 35V. The designer chose to use the same value cap for all three locations.

    The CP1-CP2 capacitor should be rated for at least VM.
    The VCP and VGD should be rated for 16V minimum.
  • 0 in reply to Rick Duncan
    Guru 12155 points
    Hi Rick-san,

    Thank you so much for the information.
    I understood but I need more about the detail of the #2 question.

    I would like to know the affect which is caused by too small capacitor and too large capacitor.
    (Our customer is asking it as well.)

    Best Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Guru** 114905 points
    Hi Hamamoto-san,

    For the charge pump, there are two concerns.

    One is the absolute value of the VCP capacitor
    A variation of +/-50% should be OK.


    A second is the ratio of CP1/CP2 to VCP.
    If the CP1/CP2 capacitor becomes much smaller than the VCP capacitor, it will have to pump more to maintain the charge.
    If the CP1/CP2 capacitor becomes much larger than the VCP capacitor, the VCP voltage can spike when the CP1/CP2 cap is injecting charge.

    As long at the CP1/CP2 to VCP capacitance ratio remains between 2:1 and 1:2, there should be no problem.
  • 0 in reply to Rick Duncan
    Guru 12155 points
    Hi Rick-san,

    Thank you.

    Best Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    Guru 12155 points

    Hi Rick-san,

    Can I ask the following question in addition?

    #1: Regarding VCP and CP1/CP2 and VGD capacitor,0.22uF +/-50% tolerance will be acceptable as you mentioned above.Is this tolerance guaranteed the specification on the datasheet? If it is not guaranteed, is there any limitation when the capacitor is not 0.22uF but it is within +/-50%? (i.g. The output current should be less than xx A. Or something.)

    #2: If the VCP and CP1/CP2 and VGD capacitor is more than +50% or less than -50%,what does it happen?

    These question is from the customer and they are considering the behavior at abnormal case for such as DRBFM.(this is not automotive application but they need to consider)

    Best Regards,
    Koji Hamamoto

  • 0 in reply to K.Hamamoto
    TI__Guru** 114905 points
    Hi Hamamoto-san,


    #1: Regarding VCP and CP1/CP2 and VGD capacitor,0.22uF +/-50% tolerance will be acceptable as you mentioned above.Is this tolerance guaranteed the specification on the datasheet? If it is not guaranteed, is there any limitation when the capacitor is not 0.22uF but it is within +/-50%? (i.g. The output current should be less than xx A. Or something.)

    >>> This tolerance is not guaranteed in the datasheet. There is no limitation. The design team simulates to determine if the charge pump will work with different capacitance values.

    #2: If the VCP and CP1/CP2 and VGD capacitor is more than +50% or less than -50%,what does it happen?

    >>> This is difficult to determine because it was not simulated. In general, more than +50% can cause higher inrush currents during startup and may reduce the charge pump frequency during operation. Less than -50% can reduce the inrush current during startup and may increase the charge pump frequency during operation.
  • 0 in reply to Rick Duncan
    Guru 12155 points
    Hi Rick-san,

    Thank you for your prompt reply.

    >This tolerance is not guaranteed in the datasheet. There is no limitation. The design team simulates to determine if the charge pump will work with different capacitance values.

    Can I ask what you mean? Are your team going to simulate? Or your team had already simulated (done)?
    If your team are going to simulate, I should wait.

    Best Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Guru** 114905 points
    Hi Hamamoto-san,

    These simulations are completed early in the design cycle.
  • 0 in reply to Rick Duncan
    Guru 12155 points
    Hi Rick-san,

    Thank you.
    I understood that the simulation of the capacitor variation already had been completed early in the design cycle.

    Best Regards,
    Koji Hamamoto