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TPS54JA20: Internal VCC differences and effect on UVLO and efficiency

franziskus
Expert 7678 points
Part Number: TPS54JA20
Other Parts Discussed in Thread: TPS548A29, TPS548A28,

Team,

my customer has a question about the comparison of the follwoing three devices with regard to the internally generated VCC (via internal LDO): TPS54JA20 vs TPS548A28 vs TPS548A29

There is the difference between 3.3V and 5V, but according to datasheet, neither UVLO nor efficiency really differ between the devices.

Can you explain the reasons for that?

BR

  • 0
    TI__Prodigy 280 points

    Hi Franziskus,

    The first thing to note is that the TPS54JA20 has a reference voltage of 0.9 V and has a different fault response than the TPS548A28.  With regards to the Vcc situation, the TPS54JA20 and the TPS548A28 are identical.  

    As to your main point: the 4.5V Vcc of the TPS548A29 will reduce the LDO power loss from the 3V Vcc of the TPS548A28/TPS54JA20 and it will saturate the MOSFETs more, which will slightly lower the RDSon of both the High and Low side MOSFETs.  Both of these will result in a *slight* increase in efficiency.

    Unfortunately, the datasheet graphs are a bit hard to compare with each other, but the TPS548A29 is a more efficient part, maybe about 1%.  

    As per the UVLO, even with the 4.5V Vcc, we still want the part to function with a Vin down to 3V, so the UVLO wouldn't change.

    Let me know if this makes sense.

    -Carson Harraman

  • +1 in reply to Carson Harraman
    TI__Expert 7678 points

    Thanks for your detailed answer Carson! This helps!

    BR