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TMCS1100: TMCS1100 with MAX78630 - Current Measurement.

Mehmet Gunce Akkoyun
Prodigy 75 points
Part Number: TMCS1100

I am developing a "irrigation pump" energy analyzer. Irrigation pumps are controlled with Wye-Delta controller (in my country, soft starters are not used common). In these controllers system have X/5 current transformers for measuring current (energy meter or ampermetre) for reason of high current (more than 100A).

  • X/5 CT is the blue component in the picture.
  • Schematic is also below.

To measure all electrical parameters I use MAX78630 energy measurement IC. With these IC I use voltage dividers for measuring the AC voltage. And also use second CT for measuring current. MAX78630 Schematics. I also use second CT for modulating X/5 current transformer output to MAX78630 CST1005.

Question:

I want to change current sensing inputs for more accrue measurements. 2 way to do these.

1- Shunt resistor. 2- Current Measure IC.

  1. May I use these type of shunt with my design ?.
  2. May I use these type of measurement IC with my design ?.
  3. Which one is the best way.

Technical Abstract

  • System have 2 CT
  • First CT is (as shown on image) X/5 0.5 class current transformer. Seconder current is 5 A. Primer current is more than 100A.
  • Second CT is (given by link CST1005) for modulating 5A to max78630.
  • I need more than 0.5 Class accuracy.
  • 0
    TI__Mastermind 18790 points

    Mehmet,

    Both devices you posted have the ability to be used in such a system, with some advantages and tradeoffs of each. I wouldn't say one is necessarily better than the other, but they are useful in different areas for different use cases. 

    The TMCS1100 you linked to may be used here, and has built isolation, so you could implement this device on the primary if necessary. However, the device is only capable of up o15A of continuous RMS current over temperature, so this may be a disqualifier if you are looking to implement a solution at your 100A node. Keep in mind that while this is a "shuntless" device, there is still a small power draw, as the lead frame of the device is ~1.6mΩ, and this heat generation is what places the 15A restriction on the device. As you can find in the datasheet, this value may be increased if ambient temperature is well controlled, or if the current being measured is duty cycled. Finally, the device comes with a BW limitation of 80kHz, so if this is a high speed application, this will also have bearing. 

    The second product you link to is simply a shunt. This is a high power dissipating resistor that would convert the current to a voltage via Ohms law. You would need additional circuitry (potentially a driver/buffer, and an ADC) to quantize that information. Again based on where you are looking to implement here, you may also need to find a way to isolate this information over the isolation barrier to the secondary. As this is simply a DC passive component, apart from parasitic inductance from the leads of the device, this will be relatively large BW, and therefore superior if this is a high speed use case.

    Let me know what questions you have.