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UA78: About TO-263 package thermal information.

Kazuya Nakai59
Guru 21315 points
Part Number: UA78

Hello guys,

One of my customers use UA7805CKTTR for their many mass-productions.

Recently, they received PCN which informs UA7805CKTTR will be discontinued.
The PCN recommend to use LM7805SX/NOPB as a alternate device.
But they checked thermal information of both devices and they found the big difference of R theta JA.

R theta JA
UA7805CKTTR    : 25.3 degree C/W
LM7805SX/NOPB: 44.8 degree C/W

They think they can't use LM7805 as alternate device of UA7805CKTTR.
Also they couldn't find any similar performance device in TI LDO products which has similar R theta JA.

At this moment, they have the following questions.
Could you please give me your reply?

Q1.
Why is the reason of R theta JA difference even if both device package is same?

Q2.
Do you have any product except LM7805SX/NOPB?

Your reply would be much appreciated.

Best regards,
Kazuya.  

  • 0
    TI__Expert 6640 points

    Hi Kazuya-san,

    Kazuya Nakai59 said:
    Why is the reason of R theta JA difference even if both device package is same?

    While package is arguably the largest determining factor of LDO thermal resistance, it is not the only factor. Die size and device BOM (ex. bond wire material, number of bond wires used, bond wire connections, use of conductive vs non-conductive die attach, etc.) also impact RθJA. So, the reason RθJA is higher for LM7805SX/NOPB vs UA7805CKTTR despite both devices being in a TO-263-3 package is due to a combination of die and BOM differences.

    Kazuya Nakai59 said:
    Do you have any product except LM7805SX/NOPB?

    I can try to find another device with lower thermal resistance value as an alternative. Can you please help provide the socket requirements (max and nominal VIN, max and nominal IOUT)? This will help me evaluate if there are options outside of LM7805SX/NOPB that will work for this particular application. I don't see any pin-to-pin options other than LM7805SX/NOPB right now, based on 30V+ input and 1.5A load current rating. We should have more options depending on if a lower current rating is sufficient.

    Regards,

    Kelsey