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DRV421: Consultation of TI fluxgate current sensor chip

user1932012
Intellectual 750 points
Part Number: DRV421
Other Parts Discussed in Thread: DRV401,

I have the following questions about fluxgate current sensor modulation chip, please refer to, thank you!

1, the following figure "parameter list" DRV401 can be applied to 1A primary rated current Ipn, how to change the value of peripheral resistance Rshunt to detect 1A current? Taking 1A as an example, how to calculate the resistance value of Rshunt? What is the current range that DRV401 can test?

2, how to determine the primary current range that can be detected from the parameters of the modulation chip data manual?

3, why is the ERROR pin in the chip connected to the Vout pin?

4, according to the data manual, the over-range pin should be raised, but why can the over-range pin be suspended in the application circuit?

5, the REFin pin is connected in series with a resistance to the REFout pin. Must the sum of resistance in series be 4 times Rshunt resistance?

6, according to the data manual, the gain of the chip is 4. How can the gain of 1.2V/A be realized by changing the resistance value of the peripheral circuit?

7, why do some circuits connect the / PWM (19PIN) pin to the R-C-R (T filter) and then connect the series capacitance C to the IAin2 pin? And some application circuits put the pin empty?

1.docx8, the following is the product Ipn=1A chip application structure diagram, compared with the DRV401 application example is consistent, but compared with the DRV421 application diagram is inconsistent, the DRV421 application routine connection is two red circle connection exchange, what is the reason why the two chips are inconsistent in the red circle position connection?

  • 0
    TI__Mastermind 27715 points

    Hello User,

    Thank you for your interest in DRV421. Our Fluxgate expert returns to the office on Monday and will adrdress your questions then.

    Best regards,

    Ian Williams
    Applications Manager
    Current Sensing

  • 0
    TI__Mastermind 32260 points

    Hello User

    Below are my responses.  

    1.The DRV401 can drive the Icomp pins to 250mA with VDD = 5V. The voltage swing on the H-Bridge is 4.2 VPP so therefore you will be limited by the number of loop in your compensation coil and the resistance of your compensation coil.  At 1A you will not have much problems with the resistance of your compensation coil.  The compensation current will be equal to Primary current /  #Windings.  The output voltage will then be equal to this current muliplied by Rshunt and then by the gain of the Diff Amplifier (4) referenced to the Vref pin.

    As your example if 1A and you have 1000 Windings.  Rshunt  = 100.  Compensation current 1A/1000 = 1mA.  Vout = Compensation Current*Rshunt*Gain = 1mA*100Ω*4V/V = 400mV

    2.  This will be dependent on your compensation coil and its properties.  You could run across different limiting factors.  One is the number of windings could increase your compensation resistance therefore you will be limited by the voltage drive of 4.2V.  I have attached an excel sheet that goes through the math and uses devices that are similar to the DRV401.  You can increase the drive with external circuitry see TIPD184

    DRV401_Max_Primary_Current_Calculations_with_no_external_circuitry.xlsx

    3.  Where do you see this example.  The reason you would do this is to make sure your output gets pulled to zero if there is an error condition.  This way you only monitor the Vout pin.

    4.  This is an alert pin.  You can have this floating if you would like but then you will not ever know if there is an over-range condition.

    5.  This is to eliminate some gain error cause by Rshunt.  There is an explanation in the datasheet.  If you can deal with a little gain error or if Rshunt is low you can ignore this.

    6. For easy you can lower Rshunt to get your desired gain or place a voltage divider at the output.  Please realize the output is reference to Vref.

    7.The datasheet explains this is for compensation of the probe oscillator ripple.  It is not required as stated in datasheet.

    The connection to the AINP and AINN can be interchanged as can the direction of the current through the core.