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DRV8840: Capacity between CP1 and CP2 as also between VCP and VM

Xavier Queffelec
Intellectual 310 points
Part Number: DRV8840

Dear support Team

 

I found two different sources of information concerning those capacities in the datasheet – Revised December 2015 (should be the actual one)

On page 18 – 10.1 Layout Guideline – the following is written:

  • "A low-ESR ceramic capacitor must be placed in between the CP1 and CP2 pins. TI recommends a value of 0.1μF rated for VM."
  • "A low-ESR ceramic capacitor must be placed in between the VM and VCP pins. TI recommends a value of 0.47μF rated for 16 V."

Now on page 14 – 8.2 Typical Application: I can found:

  • 10nF instead of 100nF for the capacity between CP1 and CP2 as 100nF instead of 470nF for the capacity between VCP and WM
  • On the CPG005 document – evaluation board – 10nF is also used between CP1 and CP2 and 100nF between VCP and VCMA but no resistor with 1M Ohm.

Please can you help me finding which version is correct, or what you will say, its better?

 

Can you also help me concerning the value for the bulk capacity?

  • In your provide document you are using 100µF – datasheet on page 14 as the CPG005.
  • On page 17 – 9.1. Bulk Capacitance Sizing – you give a lot for factors which influence the value for this capacity but you didn’t give any equation to calculate the minimum and maximum capacity that should be use.

Can you provide me more information about it?

 

Many thanks for your help.

Best Regards,

Xavier

 

  • 0
    TI__Genius 14487 points

    Hi Xavier,

    Thanks for your feedback here. The values in the layout guidelines are a mistake, and I've made a note to correct them in our next datasheet update. Please use the values 10nF and 100nF as suggested in the application section and in the Pin Functions table.

    The 1 MOhm resistor can be included or excluded. It helps to discharge the charge pump capacitor faster when the device is put to sleep.

    The bulk capacitor is meant to filter ripples and transients at the power entry point to the board. We don't spec this in the datasheet because it could vary depending on system requirements. Here are some links to information about sizing bulk capacitors I think may help.

    Input and Output Capacitor Selection

    How to select input capacitors for a buck converter

  • 0 in reply to James Lockridge19
    Intellectual 310 points

    Dear James,

    Many Thanks for your answer.

    I will have a look to the two link you send and come back to if I have any question.

    Best Regards,

    Xavier

    PS: I made a mistake, as I post two times the question - I had an error during the upload.

    So I will directly close the other topic and you can remove it, if it's possible.

  • 0 in reply to Xavier Queffelec
    Intellectual 310 points

    Dear James,

    I calculate the Bulk capacitor and I get around 220uF, so it's okay.

    I make all the connection with the chip and I have an other question concerning power sequencing as I didn't see anything about it

    On the control side I am using 5V supply for signal which are coming from my microcontroller and 24V on the motor side.

    For powering the devise up should torn on the 24V (VM) first or is it possible to have the 5V first an then the 24V?

    Many Thanks for your answer.

    Best Regards,

    Xavier

  • 0 in reply to Xavier Queffelec
    TI__Genius 14487 points
    Xavier,

    I think either order is acceptable. All the logic pins have internal pulldowns. This is good because if you power the DRV8840 before you power the MCU, all of the inputs are low and the outputs are high-impedance. If you power the MCU before you power the DRV8840, then I recommend setting all the MCU GPIO to the DRV8840 low so that when the DRV8840 is powered, it is in reset mode. Once then 24-V power rail reaches its correct level, then you can take the device out of reset and sleep mode then enable it.
  • 0 in reply to James Lockridge19
    Intellectual 310 points
    Dear James,

    Many Thanks for your answer.

    I understand the Issue with the reset and the sleep mode - both aren't control directly from my microcontroller - just enable (IN1) and phase (IN2).
    I took care about the reset pin, that this one can be put it low again (manual fault acknowledge) and stay in reset until both 5V and 24V are not present.
    Concerning the sleep pin, I just use a pull up to 5V so in this case it will better to keep my 5V off till the 24V become valid.

    Many Thank again for your help.
    Best Regards,
    Xavier