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DRV8320: Pull up Resistor

Laura Shuey
Intellectual 810 points
Part Number: DRV8320

we are testing our first prototypes with the DRV8320 now and found that we need a pull-up resistor

of about 1.5kOhm on the SDO line of the SPI interface. While the need for a pullup on this signal is mentioned in the datasheet I am a bit concerned about the low resistance value actually required.

I would like to know about the reason for this low value and what I need to consider for the 2nd prototype regarding the value of the resistor in combination with the maximum allowed bus speed.

  • 0
    TI__Expert 4650 points
    Hi Laura,

    For the SDO Pin you can use a value closer to 10k Ohm if desired, we don't have a recommended value in the datasheet. The value chosen for this pull up is dependent on your system design for a needed bus length, bus speed, and noise immunity. You can roughly approximate the value needed for a given bus frequency by using a simple (2 * Pi * R * C) calculation to determine the needed pull up resistor.
  • 0 in reply to Phil Beard
    TI__Intellectual 810 points
    To estimate the frequency I would need to know the “C” in the formula presented above which is most likely mainly defined by the internal capacitance of the DRV on the pin SDO. Can you give me a value?
  • 0 in reply to Laura Shuey
    TI__Guru** 114905 points
    Hi Laura,

    The "C" is the complete path of the SDO (output, trace capacitance, and input capacitance). I suggest you start with a 50pF.

    By using a slower SPI speed, the C can be measured using a scope.