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Original question:

TIDA-01371: The pull current of a capacitive load from a pulsed source

TIDA-01371: some questions about equation(1) and TIDA-01592

BX27
Genius 3900 points
Part Number: TIDA-01371
Other Parts Discussed in Thread: TIDA-01592

Hi @Sanjay Pithadia  

This TIDA-01371 and TIDA-01592 ref design is very useful. some questions to consult.

nice discussion in the orignal post is :https://e2e.ti.com/support/tools/simulation-hardware-system-design-tools-group/sim-hw-system-design/f/simulation-hardware-system-design-tools-forum/896024/tida-01371-the-pull-current-of-a-capacitive-load-from-a-pulsed-source?tisearch=e2e-sitesearch&keymatch=TIDA-01371#

1.  For equation(1), I agree that, from energy perspective, "the equivalent power related either positive or negative voltage source is C*V2*f, instead of 4*C*V2*f ". but the doc seems unchanged.

But, Can we see this question from impedance perspective:

HV+ or HV- should provide power during 1/2 T0 ( T0=1/f)  : P = V*V/ Zc = V*V / [1 / (2*pi *f * C) ] = 6.28 * V*V* f * C. now the factor is x6.28 isntaed of x4. How do you  think?

This post also discuss this question, but the picture seems un-openable. 

https://e2e.ti.com/support/tools/simulation-hardware-system-design-tools-group/sim-hw-system-design/f/simulation-hardware-system-design-tools-forum/623156/tida-01371-clarification-regarding-the-peak-power-consumption-formula-about-multiplication-factor-4?tisearch=e2e-sitesearch&keymatch=TIDA-01371#

2. This ref design is 20A/100V, it is 2KW rather than 80W, what does this 0.8A mean in page 5 for Elastography? seems irrelevant。

Also, I did not found a 9000uF (so large) output capacitor on sch. Could you help explain?

3.  I also noticed newer ref design  TIDA-01592, which mentioned 15-30W is enough, much less than 2KW in TIDA-01371 . which one is correct? Calculation of power capabilities of HV power (especially for shear wave mode) is confusing me. maybe you could help. we are doing 128channel medical u/s. +/-100V.

Thanks very much!

  • 0
    TI__Genius 12961 points

    Hi, thanks for reaching out. Let me review all your questions and get back in a day or two. 

  • 0 in reply to Sanjay Pithadia
    TI__Genius 12961 points

    Sorry for the delay in replying.

    1) For the power supply calculations, we will review internally and update the document accordingly.

    2) For 80W is continuous power. The 20A is for 1ms time only (for elastography). The design can be scaled to higher power by adding more MOSFETs in parallel. The 9000uF cap is the possible value of cap required if you don't use floating LDO scheme. In the ref design TIDA-01371 you don't need such higher capacitance.

    3) TIDA-1592 is designed for lower power - it does not support elastography mode.

    For your application, what power level do you want to support? Do you need to support elastography mode?

  • 0 in reply to Sanjay Pithadia
    Genius 3900 points

    Hi Sanjay

    We need to support elastography mode(specificaly, shear wave), and the problem we are facing is how to determine the power we need(average and peak power). 

    1. OK, I can  wait.

    2. I am reading your manuscript. If 9000uF cap is not needed when using floating LDO scheme, why did you use 9000uf derived out 0.9V Vdip and then ase 9000uF derived a 18A charging current, as I marked out in blue. i do not understander very clear. hope you could help expain. thanks.

    3. I indeed found TIDA-1592 user guide mentioned that it supoort elastograph mode. kind of confusing..

  • 0 in reply to BX27
    TI__Genius 12961 points

    Hello,

    2. The calculations are valid if you don’t have a floating LDO scheme. If you want to support elastography mode with your switched-mode power supply only, you will need 9000uF cap to achieve 0.9V dip. To replenish it in 10ms, you will need 18A current.

    I want to make sure that this calculation is showing that you need bigger cap if you don’t have floating LDO scheme.

    3. It needs to be corrected; we will update it. Only TIDA-01592 cannot be used for elastrography. It needs to be updated with right components and should be paired with floating LDO scheme to support elastrography.