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# ADS8588SEVM-PDK: how to select the value of the relevant device？

Other Parts Discussed in Thread: TIDA-00498, TIDA-00834, TIDA-00128, TIDA-00493

in the article ，  tiduco9a.pdf，I have some question below

first，in the  table 3，I want to know how to decide the value the load resistor which is 13.778,why it not 30 or other？for example，I  know the max input 7.07 from 10/1.414） why make the op gain is 9.92  why the primary   current  is  129.318 A ,why not  120A,why  how dose  these data  get  from？

second， about  the two stage RC filter，which frequency do they filter ，is there a article describe  more detail？

third ，for example if my ADC input max voltage is 0~3.0V，what the range of the op output is fit？0.5~2.5  or 0~3  or 0~2.5，now my cicuit below ，the output of the op is 0.5~2.5，I have no idea。IF i want to get a range from 0~2.5V，how should i modify  the circuit above？how to select the burden resistor？my primary current is  50hz AC 1A~5A  .the RC filter  between the two op，how to decide the value？different circuit has different resistor to obtain gain，is there any principle to obey to decide the value of the resistor？

fourth，I found that in the circuit above  the signal out from transformer go into the positive pole of the op。

but in the the circuit below ，the signal  out  out from transformer go into the negative  pole  of the op，why？which has a better performance？

• Hello user4973896,
This tiduco9a.pdf is a Reference Design from system team, I will involve the authors to answer your questions. Thanks.

Best regards
Dale Li
• So many days have passed，why still  no  people  answer  me ！！！！

• Hello All

Here are my inputs to your questions

first，in the  table 3，I want to know how to decide the value the load resistor which is 13.778,why it not 30 or other？for example，I  know the max input 7.07 from 10/1.414） why make the op gain is 9.92  why the primary   current  is  129.318 A ,why not  120A,why  how dose  these data  get  from？

The selection of the burden resistor depends on the Current transformer (CT)  linearity for the selected load, gain amplifier stage and the input current range.

The CT selected linearity performance within class 0.2 can be achieved with 15R burden. The target was to measure 120A with tolerance for component variation that can be calibrated and so the design has been configured to measure up to 129A.

Section 2.8 provides more details for your reference. Please note that standard values of resistors are preferred for optimized cost.

second，  about  the two stage RC filter，which frequency should they filter ，is there a article describe  more detail？

The RC filter depends on the application.

Can you please provide more details on the application (End Equipment details) for me to provide the required input.

The Filter stage depends on the fundamentals and the number of harmonics of intrest

third ，for example if my ADC input max voltage is 0~3.0V，what the range of the op output is fit？0.5~2.5  or 0~3  or 0~2.5，now my cicuit below ，the output of the op is 0.5~2.5，I have no idea。

Can you please provide more details on the questions.

The Op-amp output must be same as the ADC range.

Use a Rail-to-Rail output type Op-amp for providing the required gain.

You can consider TIDA-00834, TIDA-001214, TIDA-00128, TIDA-00493, TIDA-00498 for choosing the gain amplifiers