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UCD3138FW-BIDI: About initial_setup function

Parrish Huang
Prodigy 110 points
Part Number: UCD3138FW-BIDI
Other Parts Discussed in Thread: TIDA-00653,

Tool/software:

Dear TI Experts,

Reference project: TIDA-00653、UCD3138FW-BIDI

I would like to ask about the calculation formula for "I_OUT_ZERO" in the initial_setup function. (file: misc.c)

1. What are the references for "6.25" and "0.64" in line 249 ?

2. What are the references for "10.24" in line 260 ?

3. Where does the range of "15000" at line 292 come from?

  • 0
    TI__Expert 6855 points

    Hello Parrish,

    I am reviewing your question and I will respond by the end of the week.

    Regards,

    Jonathan Wong

  • +1 in reply to Jonathan Wong
    TI__Expert 6855 points

    Hello Parrish,

    That section of the initial setup is aiming to set an EADC value to result in a zero current output.

    0.64 is obtained by the resistor divider for converting the ADC value to the DAC value (1.6V/2.5V = 0.64)

    6.25 is used to convert the ADC reading to the equivalent DAC value

    10.24 is used to convert the EADC error value to the EADC DAC value

    15000 is used when to prevent the op-amp from locking up in startup. There is a case when 12V is applied first and then 48V is applied that locks up the op-amp. See the schematic below. The 16VS rail is still 0V but the voltage at pin 2+3 is 12V. So, the output of the op amp will be very high (~16000) so the 15000 detects this case. 

    Regards,

    Jonathan Wong