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UCC14240-Q1: Application Note Equation and Calculation Tool match

Patrick Ruf
Genius 4810 points
Part Number: UCC14240-Q1
Other Parts Discussed in Thread: UCC14240EVM-052

Hi,

I try to understand the Application Note "UCC14240-Q1 Simplifies HEV, EV, Bias Supply Design for Isolated Gate Drivers" (SLUAAH0).
In chapter 7 on page 13, Equation 10 gives 3.5uF as minimal capacity for CVDD in series with CVEE.

If I put all the values into the Design Calculation Tool (Version 8) I get a minimal value of 0.967uF for CVDD (COUT2min) and minimal value of 2.9uF for CVEE (COUT3min).
Series connection of those two results in 0.725uF which is far from 3.5uF.

Equation 18 from the Application Note seems to be implemented into the Design Calculation Tool.


Ripple in the Application Note is 0.5Vpp. So I put a value of 3.333% in the Design Calculation Tool for the desired ripple percentage.

How does the Design Calculation Tool calculate the value for COUT2min?

Best regards,
Patrick

  • +1
    TI__Mastermind 25355 points

    Patrick,


    There are several improvements that have been introduced to the Excel Calculator Tool version 8. The capacitor calculation in v.8 has been updated in the time since the Application Note was first released. The application note was written to correspond to Excel Design Tool, version 1. With regards to capacitor calculation, the biggest difference between version 1 (Application Note calculations) and version 8 is the addition of Cout1b shown in version 8. Splitting the original COUT1 (as shown in the application note) into COUT1//COUT1b gives lower values for the capacitance CVEE and CVDD and this is what you are seeing. 

    The Excel version 8 calculations are optimized and up to date and should supersede the app note. The app note was intended to give insight into the equations used in the Excel tool and the plan is to update the app note to align with the Excel tool version 8. Thanks for raising the issue with your E2E thread contribution. 

    Regards,

    Steve

  • 0 in reply to Steven Mappus1
    Genius 4810 points

    Steven,

    Thanks for the reply.
    So I assume that the capacitor values of the UCC14240EVM-052 are also based on an older Design Calculation Tool version as there is the Cout1b missing as well.
    Is that correct?

    Regards,
    Patrick

  • 0 in reply to Patrick Ruf
    TI__Mastermind 25355 points

    Correct. The capacitor calculations used in the earlier versions of the Excel Design tool are still correct (the ratio is most important) but the version 8 Excel Tool introduces the idea of splitting the VDD-VEE output capacitor and we refer to this as Cout1+Cout1b. The result given in version 8 is a lower total capacitor value.

    Regards,

    Steve