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DRV8305-Q1: DC calibration and charge pump questions

Benjamin Balazsi
Prodigy 340 points
Part Number: DRV8305-Q1

Dear all,

I have some questions regarding the DC calibration.

  •  How long does the DC calibration take? How long is the current measurement inactive after start of the calibration? (disconnect load / shorting to GND the current shunt amplifier inupts)
  • does the offset correction take place in the driver (on HW level) or it has to be realized in software?
  • is there any application note or other document which describes the calibration in detail?

Also one question regarding the charge pump:

when the chips' Enable is set to high then there are pulses at Pin 43. The recommended 47nF capacitor is connected. The pulses happen at a frequency of 500kHz which can lead to EMC problems. Is there any way to mitigate these pulses?

Thank you very much for the answer!

Best regards,

Benjamin Balazsi

  • 0
    TI__Guru 65190 points

    Benjamin,

    Thanks for posting on the Motor Drives Forum.

    Section "7.3.5.3 CSAs: Current Shunt Amplifiers" in the datasheet discusses the calibration steps and method. I will need to ask on the timing of this.

    These pulses from the charge pump are mandatory for it's operation. This cannot be bypassed as this is the basis for the gate drive voltage. Are you seeing EMC issues because of this or are you simply checking ahead of time?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    TI__Guru 65190 points

    Benjamin,

    To clarify for the forum, no EMC issues have been observed. The Charge Pump is spread spectrum and testing we have done internally shows no significant EMC spike in radiated or conducted emissions at or around the CP frequency.

    The CSA calibration is manual on the DRV8305-Q1 in that once the CAL bit is set high for each CSA, the inputs are disconnected from the external connection and SN/SP are shorted. The resulting CSA output voltage can be read by the MCU on the SO pin and stored for later subtraction from the measured values. This being said there is no timing requirement and the only limitation is the CSA settling time (as listed in the datasheet and below).

    Regards,

    -Adam