• State Resolved
  • Locked Locked
  • Replies 11 replies
  • Subscribers 65 subscribers
  • Views 1310 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS5430 Components Question

C Stotish
Prodigy 80 points
Other Parts Discussed in Thread: TPS5430, TPS62110, TPS54160, TPS62111

Hi,

I am working on using the TPS5430 to shift from 12-15V to 3.3V.  My output current is relatively low, most likely not exceeding .5 A.  The smaller the current, the bigger the inductor needed.  Using the datasheet and corresponding equations, an inductance of 63uH and a capacitance of 80uF for the output capacitor would work according to calculations.  I double checked this with Switcher Pro, which yielded 120uH and 180uF respectively.  The inductance is a minimum, so I don't want to use too small of an inductor, but the datasheet also states inductance values for use with this chip typically range from 10 to 100uH.  I double checked the example used in the datasheet with Switcher Pro, and it yielded larger values as well (Switcher Pro said 27uH and 470uF vs. the packet's 14uH and 220uF).  I don't want to use too large of an inductance value, but I definitely don't want to end up too low.  Anyone have any recommendations?  Is it possible to go too high with the inductance or should I go like 150uH to be safe? 

 

Also, after using Switcher Pro, I checked what the crossover frequency would be with the packet.  The math says 4.18kHz, but Switcher Pro says 5.1kHz on the Bode plot.  I guess this is just yet another discrepancy between Switcher Pro and the packet.  My bigger concern was that my zero ESR frequency for my circuit (15 to 3.3V @ .5 A) was 176.8kHz, which seems very high.  This was taken from the Bode plot on Switcher as well.  The packet said zero ESR should not be too far above compensation poles @ 24k and 54k.

 

Perhaps Switcher Pro isn't very accurate.  But I don't know, which is why I'm here asking.  Specs for my situation are 12-15V input, 3.3 V out, approx. .5A max load on the output.  Any help on what I should use or suggestions would be much appreciated.  Thanks.

 

Chris

  • 0
    TI__Mastermind 36110 points

    Power Quick Search returns different ICs that will be easier to design with.  I suggest you consider the TPS62110 or TPS54160 and use the EVM designs as is (including layout) with minimal modifications to get the correct output voltage)

  • 0 in reply to Matthew Day
    Prodigy 80 points

    I looked over the datasheets for both of these products.  They both look like they would work, but why are you suggesting these are EASIER to use than the TPS 5430?  They seem to require pretty similar setups.

     

    Also, the TPS5430 was chosen, as it worked well in another system we use.  I would prefer to stick with this chip, unless it is not capable of working stabily.

     

    I am considering using the 62111 you suggested.  However, the datasheet does not contain the configuration for this chip, it contains 62112 (the 5V version) and the 62110(the variable version), but not for 3.3V.  And using SwitcherPro seems to give very different setup configurations.  Do you know where I can find this configuration?

     

    Chris

  • 0 in reply to C Stotish
    TI__Guru**** 150820 points

    The TPS5430 will work for your application and there are tradeoffs when choosing between parts.

    The TPS62111 is the lowest cost solution, as it requires a lower value inductor and it can work with ceramic output capacitors.  The IC is also cost effective.  The datasheet explains how to pick the inductor, input cap, and output cap, beginning on page 15.

  • 0 in reply to C Stotish
    TI__Guru**** 191445 points

    The TPS5430 uses internal compensation and voltage mode control.  In general the output filter components must be chosen to so the LC filter double pole and ESR zero pf teh output capacitor cclosely align with the poles and zeros of teh internal compensation.  That being said, there are many alternate configurations that will yield acceptable stability.

    As far as the inductor value is concerned, the datasheet uses a well known criteria for calculating the minimum inductance.  It is based on teh maximum allowable ripple current as a percent of the output current (Kind).  Typically Kind is chosen as 20 or 30 %.  Of course, this is mostly a user preference.  If you can tolerate more ripple current then you ar free to reduce the inductor value.  The TPS5430 is non-sysnchronous, so that may result in operating DCM over more of the load  conditions.  Once the inductor value is chosen then the output capacitor is chosen to align the double pole near teh second zero of the internal compensation.

    The data sheet uses very simple model for estimating the crossover.  Switcherpro uses models the actual output filter and calculates teh crossover accurately (within the limits of the L and C parametric data.  I have used switcherpro quite abit with these parts and find the modeling to be accurate, but sometimes like to fine tune the component selection to my own preferences.  You can use teh "what if" page to experiment with different output filters and see the resultant loop response.

  • 0 in reply to Chris Glaser
    Prodigy 80 points

    My apologies. I did not see that at first glance.  So I would simply use the 62110 setup for 3.3V with the 62111 chip then, making sure that LC>= (22e-6 * 6.8e-6), correct?  Also, what values do you suggest for R5 and R6 across the input.

     

    I need to see what a few other ppl want for this design, to see if they are ok with switching to the 62111.

     

    If I did want to stick with the TPS5430, what would you suggest for inductance and capacitance values?  (Read first post again).  My values are 12-15V input to a 3.3V output @ 0.5 A. I just want to make sure I don't go too low/too high on any values.

    I apologize for any inconvenience I've caused.  I am an intern, and want to make sure this works, as it is going to be used for a military project and needs to be built for industrial strength. 

    Thanks.

  • 0 in reply to C Stotish
    Prodigy 80 points

    My last post was @ Chris.

     

    @ John:  Thanks.  That explains the discrepancy in the crossover frequencies from hand calculations to switcher pro.  I think the values chosen by Switcher Pro would be relatively good design choice then.  My last concern: that high ESR zero frequency.  Switcher Pro shows this to be 176.8kHz.  Is this value acceptable?

     

    Thanks again.

  • 0 in reply to C Stotish
    TI__Guru**** 191445 points

    Can you send me or post your switcherpro design?  I'll take a look at it.

  • 0 in reply to C Stotish
    TI__Guru**** 150820 points

    Yes, design for a 3.3V output but use the TPS62111 IC.  Yes, keep LC >= 6.8 * 22 * e-12.

    R5 and R6 set a threshold for using the low battery comparator.  Per the block diagram on page 6, this is an uncommitted comparator.  If you need a comparator for your design, this is one that you can use.  If you don't need a comparator, simply ground LBI and leave LBO floating.

  • 0 in reply to Chris Glaser
    Prodigy 80 points

    @ John:

    https://analogtools.ti.com/SwitcherPro/Main/MainPage.aspx?PartNumber=TPS5430&VinMin=12&VinMax=15&Vout1=3.3&Iout1=0.5&design-TPS5430

    You can also get to it by using the Design Now feature on the product's page and using 12, 15, 3.3, and .5 for the min input, max input, output voltage, and output current respectively.

     

    Like I said, Switcher uses around double the inductor and output capacitor values I calculated, but it could be selecting for best response, not just the minimum.  Like I said, my largest concern for Switcher's results (120uH and 180uF) is the zero ESR freq.  On the loop tab (Bode plot), it is showing as 176.8kHz. 

     

    Thanks

  • 0 in reply to C Stotish
    TI__Guru**** 191445 points

    Switcherpro is choosing a larger inductor value so it can use a smaller output capacitance.  I would use 68 uH inductor and 100 uF tantalum output cap with 75 mohm ESR such as AVX TPSC1070100075.  This should yield ideal results.

     If the output ripple is too large you can add a ceramic 10 uF cap in parallel with the 100 uF.

  • 0 in reply to JohnTucker
    Prodigy 80 points

    John,

     

    Thanks a lot!   I originally selected almost those exact values, and SwitcherPro made me question myself.  You can ignore my other post.  Thanks again