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DRV421: how to understand the low impdance of H bridge at high frequency

Ocean Lee
Prodigy 90 points
Part Number: DRV421

Dear TI engineer,

I am now reading the datasheet of DRV421. It mentioned that the impedance of H bridge is low when the frequency is high. I can't understand it, how the the secondary coil current of transformer through?

Could you help to explain it?

  • 0
    TI__Mastermind 27715 points
    Hello Ocean,

    Thank you for your question. Our engineers will analyze and respond when we return to the office on Monday.

    Best regards,

    Ian Williams
    Applications Manager
    Current & Magnetic Sensing
  • 0
    TI__Mastermind 29280 points

    Hello Ocean,

    Thanks for using the forum to ask your question.  So at higher frequencies the primary and secondary act as a current transformer. See DRV421 System Parameter Calculator for examples of the response.  This assume you magnetic core material can respond to higher frequency signals.  I have attached a screen shot below.

    At lower frequencies the DRV421 measures the field and sends a current through the compensation coil.  This does take time and the part must sample the field and make the determination if the compensation current must increase or decrease to null out the field. 

    At higher frequencies the magnetic core behaves like a current transformer.  So the compensation current is Primary Current/ Number of Winding on Compensation Coil.  The H-Bride allows that current to flow and allow the magnetic coupling to behave as a transformer would.  At this point the current is not being driven by the H-Bridge but allowed to flow through and then will be measured across the shunt resistor.