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DRV5056-Q1: the method of DRV5056 RC

lI OWEN
Prodigy 10 points
Part Number: DRV5056-Q1
Other Parts Discussed in Thread: DRV5056

Tool/software:

Hi IT engineer:

  I'm applying DRV5056 on measuring distance between a platform and sensor ,  but we found the readings from DRV5056 is very unstable. we want to adopt the RC to decrease this instability refer to the DRV5056 instruction. This RC need to be used with a resistance .Could IT engineer please provide some advice on the Value of the resistance we should adopt.

                                                                                                                                                                                                                               Thanks for your advice.

  • 0
    TI__Mastermind 20980 points

    lI OWEN,

    Adding a filter to the output of DRV5056 should help you reduce the output noise of the device.  The selection of the resistance and capacitance will depend on a few factors.

    Firstly, the device has an output drive strength shown here:

    If the loading conditions would possibly cause the device to exceed this current then you would need to modify the resistance upward to limit the current draw.  Fortunately in most cases, the load should be the input pin of an ADC, and the device should be able to drive this.  

    The other consideration is the settling time of the sampling ADC.  The sensor must be able to drive the total capacitance of both the filter and the sampling capacitor of the ADC.  

    The two capacitances will effectively be in parallel.  You want to ensure that the settling time of the effective RC time constant is well suited to the ADC sample and hold time, and that the peak current is able to drive this signal.  If the 1mA output current is not sufficient to settle the voltage within the sample time of the ADC, then you would need to adjust the capacitance downward to get a more reliable result.

    The output bandwidth of the device is 20kHz, so it should be safe to target setting your filter frequency at least this low, but you may want to set the corner frequency even lower to achieve better noise reduction, but if you set the corner frequency too low, then the voltage may not sufficiently settle in time for your ADC.

    Thanks,

    Scott

  • 0 in reply to Scott Bryson
    Prodigy 10 points

    Hi Scott:

          Thanks for your comments. It is very helpful to our measurement. If the current would not exceed the range in the format, whether we could set the resistance to 0?                                                                                                                                                    

                                                                                                                                                                     thanks for your advice.

  • 0 in reply to lI OWEN
    TI__Mastermind 20980 points

    Yes, in theory you could.  Your effective RC corner frequency [fc = 1/(2πRC) ] will be dominated by the parasitic resistance of the trace impedance and the effective series resistance of the capacitors.  Your filter will be more effective with a non-zero value since you will be able to set a lower corner frequency.

    Thanks,

    Scott

  • 0 in reply to Scott Bryson
    Prodigy 10 points

    Hi Scott:

                Thanks for your advice!