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TLV755P: Thermal Viability of SON vs SOT-23 Package

Part Number: TLV755P

In my application, I am looking to use TLV755P. The requirements are as follows:

  • 3.3Vin
  • 1.8Vout
  • 300mA peak output
  • Output is modulated - typical on-time is 200us with four pulses every 500ms; duty cycle can be as high as 5%
    • Pd,peak = 450mW, 5ms max
    • Pd,avg = 23mw (D < 5%)
  • Board will have 4 or 6 layers with multiple ground layers
  • T,PCB,max = 85C (doesn't rise significantly during on time)

I am trying to determine the thermal viability of the SON and SOT-23 packages. I have a general idea of how Rja and Rjb are characterized and how they differ from one another. I also see from one of our app notes that the Rja of the SOT-23 package of TLV755P can be much improved on a well-designed board. Without the ability to measure Rjb on the application PCB, it's my understanding that an analysis using Rja makes more sense. However, both the SOT and SON Rja values from the datasheet lead to the disqualifications of these devices from the application (Tj > 125C).

I'm looking for a sanity check here. Do you see any issue using this TLV755P in this application? Further, do you have any guidance on how to conduct a meaningful thermal analysis with the information available?

Thanks,

Brian

  • Hi Brian,

    My instinct tells me that this is possible, but we would need to do a little bit of work to determine the thermal impact.  It might be easier to make a measurement using an EVM.  The multi EVM that we have for the DQN package is not the best thermal design possible, so if we can show that this works on that EVM then you should be okay in practice.  I need some clarification on your requirements before I can set up the test.

    1. "output is modulated" - please confirm whether you mean the load current is modulated, or that you are not enabling / disabling the device using the enable pin.

    2. 4 pulses at 5ms max would yield 20ms total, which is 4% max of 500ms.  Did you mean 4% max? 

    3. Assuming the load is being modulated (and not the enable pin), can you provide a load profile?  This is how I am interpreting your requirements, but I can see several ways to read them so please comment accordingly.

    Thanks,

    Stephen

  • Hi Stephen,

    Thanks for your response. I will work on getting some more information on the load profile and report back.

    Brian

  • Sounds good, thanks Brian.

    Thanks,

    Stephen