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CCS/TIDM-BIDIR-400-12: ADC,

Part Number: TIDM-BIDIR-400-12

Tool/software: Code Composer Studio

Hello, again.

Thanks to your help. I can keep following the TIDM-BIDIR-400-12 reference design. 

Today, I got a problem with ADC. 

As I can see the tiduai7.pdf, Page 36, figure 44, I'm testing the buck mode open loop. 

In figure 44, ADC for input voltage/current, output voltage/current is referred Gui_Vfbin, Gui_Vfbout, Gui_Ifb, Gui_Iout respectively. 

As you see that page, it said output power is 72[W](6A,12V)

I have a question about this power. In figure 44, input power is around 182.9[W] and output power is 72[W]. 

I think this input current for ADC doesn't make it sense.

The figure below is my result.

In my Hardware, Power supply for input indicates 390V/0.21A, Electric Load indicates 2ohm/5.448A. So it matches input current for ADC I think. 

Another question is In real hardware, 5.448A is correct, But in real time ADC indicates the double value of it. (I changed the phase, rechecked the value, it is almost the double)

I think my current to voltage circuit is the problem. In tidrhs9.pdf, 

This is the before filter circuit for output current(. 

If my ADC values are doubled compared with the real value, where and what can I fix the circuit? If is not the problem of my circuit, what can you recommend for my problem.

Thank you for your help. 

  • This is my trial for my problems.
    1. Desoldered the shunt resistor(R27=0.0005ohm), removed over-soldered lead, soldered again. (For the accuracy of measuring)
    2. I adjust the value on Bi-dir-Main.c file , line 184, sub_adj=8900;
    I tried to increase this value by 11000, then my adc value is right compared with real hardware.

    Am I go the right way to fix my problem?
  • Adjusting sub_adj is not a solution I think.
    In code, adc result * 8 value is Gui_iout.
    After I checked CS_LV value in hardware, compared with simulation result, is exactly doubled.
    I think some of the value of resistor I soldered is different from the design.
  • Hi Kyoungtak,

    I am sorry for the delay. Yes, the Gui_Ifb value is not very accurate mainly because of the low power operation. Your result does look much better.

    As for the ADC result being double the actual value, please refer to the Bi_dir_Calculations.xls spreadsheet in the Docs folder. Make sure your circuit component values match with those listed here. Have you made any changes to the code?

    Hrishi

  • Thank you for your help and reply. 

    after you mentioned Bi_dir_Calculation.xls, and code, I double checked the value and code, But it is all right. 

    While I soldered the components, I checked all the components value. So that won't be wrong. 

    One the I got the strange thing is. the Voltage from the current sensing circuit. I'll explain with the next image. 

    Top of the image is the value of the hardware result of mine. The bottom is the simulation and calculation value. 

    With my measurement, IS_LV- , Voltage of pin 4 and 4 are an acceptable value compare with the calculation value. 

    But the Output voltage is far different. I think this difference of voltage makes the ADC doubled. 

    In this situation, what can I do? I can just make the ADC right value by parallel connected R39(47K/2).

    But refer to excel file, this value is used to calculate the proportion, etc. So I think parrel connected r39 is not proper solution. 

  • One thing I found from excel file is the equation for Ioutmax. 

    From excel file, Ioutmax = (VfsvADC-Offset at ADC i/p)/(Rsense*U5 Gain magnitude)

    Equation above means (Ioutmax*Rsense)*U5 Gain magnitude PLUS offset at ADC i/p equals 3.3V

    But I think as I can calculate with the equation...

    Offset MINUS (Ioutmax*Rsense)*U5 Gain magnitude -> This is correct I think. 

    Could you explain to me which point I missed or started to fo wrong way? 

    And plus, Could you explain the equation image file from the excel file I attached?

    I missed the point after Gshift. 

    Thank you. 

  • I finally find my mistake.
    Because the direction of current for IS_LV- is minus ,the direction of voltage should be opposite.
    Offset of my harware CS_LV voltage is 1.6V , 10A output current condition, 2.5883V.
    So I realize my shunt resistor's measuring voltage is too high.
  • Kyoungtak,

    I am glad you were able to solve this. Thanks for letting us know.

    Hrishi