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PTN78060W: Switching Regulators in Series

Dean Rasmussen
Prodigy 10 points
Part Number: PTN78060W
Other Parts Discussed in Thread: PTN78000W, TPS62182, PTN78000A,

Hello,

I have a existing system where I have a fairly complex power design where I use Switching and Linear regulators to create about 15 different supply rails ranging from -5.5V to +8V from a 12V AC-DC converter (brick).  For the switchers, I use the PTN78000W (+8V), PTN78000A (-3.5V and -5.5V), and TPS62182 (+3.3V).  These switches power my circuits and/or power linear regulators.

For my next project I need to add 24V support on top of the existing power sub-system.  I plan to use a +24V AC-DC converter and the PTN78060W to create a 12V supply rail which powers the above existing power sub-system. 

Questions:

1) Do you see any problems having the PTN78060W output driving 4 other switchers?  

2) Or would you recommend the existing PTN78000W/A get powered from the +24V instead of +12V?  The TPS62182 has a Vinput limit of 15V so I would still have to use the PTN78060W 12V output power this switcher.

3) Do you have any App Notes or experience minimizing the noise of the switchers hammering back onto the +12V (or +24V) AC-DC converter inputs?  On my existing design I see some problems which I suspect are coming from my design and/or layout.  I have added the PI filters as recommended in the PTN78000 datasheet.

Thanks

Dean

  • +1
    TI__Genius 10695 points

    Hello,

    1.) As long as the total input current of all 4 switchers powered by the PTN78060W is less than the maximum load current of the device then I don't see issue with this configuration. You can estimate the input current of the switchers by generating designs in Webench and observing the input current or else use the efficiency plots found in the device datasheets to estimate input current. 

    2.) Buck converters tend to operate with higher efficiency when the difference between input and output voltage is smaller, for example you'd expect higher efficiency for 12Vin to 5Vout than for 12Vin to 3.3Vout for the same load and switching frequency. 

    3.) This app note offers a starting point for designing your input EMI filter: AN-2162 Simple Success With Conducted EMI From DC-DC Converters (Rev. C) (ti.com) Layout is crucial for generating EMI compliant designs. If you share screenshots, I can help review your layout. 

    Regards,

    Harrison Overturf 

  • 0 in reply to Harrison Overturf
    TI__Genius 10695 points

    Hi Dean,

    I haven't heard from you for some time so assume this issue is resolved. 

    If this is not the case please post a reply. 

    Regards,

    Harrison Overturf