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# TIDA-01063: PCB Rogowski Coil Design

Part Number: TIDA-01063

I am looking at the TIDA-01063 reference design (document TIDUBV4A) as a starting block for developing an over current sensor in the DC leg of a half bridge high frequency inverter.  I will need a PCB Rogowski coil and an integrator circuit.  I was trying to follow the formulas in document TIDUBV4A.  I see the physical dimensions of the Rogowski  coil in Table 1 (Page 2) (coil inner and outer radius, number of turns, etc.).  Then on page 8, equation 9, I see the formula for mutual inductance.  According to Table 2, page 14, that inductance is .048 uh.  The dimension for h (dist between upper and lower trace of the PCB) is not listed in Table 1 so I am having a hard time reconciling the formula to give .048 uh.  If I assume  an h = 1.255 mm I can get 48 uh but that is far off and very high inductance.  Can someone please help me out with this?  The formula I'm using is M=(N x (uh)/(2pi))xln(Dext/Dint).  Maybe I don't have it right.

Thank you - John

• Hello John and thank you for your interest in Texas Instruments. You query has been forwarded to our Industrial Building Automation team members in Bangalore. As is such, please allow another business day for response to your query.

Best Regards,
J. Fullilove
Texas Instruments
TI Designs
• Hi John,

Thanks for using our reference design for your application, we will be glad to support to you in your design.

As per your above query my understanding is that your are trying to build current sensing for high frequency half bridge AC-DC inverter helping to achieve isolated current measurement using existing PCB itself. I assume your are trying to record average current through leg for control scheme.

For 174 turns, 1.7 mm (0.0017 m) PCB height and inner radius of 12.5 mm (0.0125 m) and outer radius of 27.7 mm (0.0277 m) we get mutual inductance of 47.07 nH approximated to 48 nH with actual measurement. (Convert mm to meter for computation as permeability is Henry per meter)

Regards,

Srinivasan

• Thank you for your reply. You information gave me the exact answer as in the publication. Now, using those same parameters I am double checking the formula for self inductance - equation 26 on page 11. My calculations come up with 8.193 uh but the publication says 8.34 uh, so I just want to confirm if maybe I have something wrong in the formula??

John
• Hello John,

We verified the self inductance using inductance analyzer and used used peak observed observed value out of 10 PCB coil sensor for doing step response simulation to get worst case delay.

Regards,

Srinivasan