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Original question:

TIDA-010237: Questions about the TIDA-010237

TIDA-010237: LPF

Maurice Katzer
Prodigy 20 points
Part Number: TIDA-010237
Other Parts Discussed in Thread: TLV7011, INA283

Tool/software:

Hello,

can you tell me, why you used this specific filter design for the filter stage. More precisely, can you tell me why you integrated two LPF in the Comparator Circuit and how were the component values for the entire filtration determined?

  • 0
    TI__Prodigy 260 points

    Can you please clarify which circuit in the user guide of TIDA 010237. The comparator circuit has INA283 feeding into comparator TLV7011 with no low pass filtering. This is to endure realtime switching of the oscillation circuit. The differential input into the current sense circuit Fig 3-4 has two RC filters. The first one has a cutoff at 55Hz this allows the AC and DC fault currents to pass with little attenuation while reducing the noise from the oscillation. The second one has a pole at 120Hz this further reduces the noise from the oscillation but introduces less delay. 

    Overall the design goal was <10% error over the full temp range. The 200 turns means a 5mA fault current is ~25 uA across the burden resistor at 60Hz while the noise from the oscillation circuit is ~6-8mA at 800Hz. The four filters used account for ~70dB of separation. 

    I recommend using TINA, Webench or TI's analog engineer's calculator to help with filter design.