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LM317M: LM317MKVURG3 replacement inquiries.

Grady Lee
Genius 4255 points
Part Number: LM317M
Other Parts Discussed in Thread: LM2940-N, LM2941, TPS7B86-Q1, TPS7A94, TPS7A20, TPS62175

Hi, TI expert.

A customer has an inquiry about a replacement for the LM317MKVURG3 (TO-252 package).

- SPEC : DC24V -> +5V, 500mA

A customer is using it with the above specifications, but since it is a TO-252 package, it occupies a lot of space on the PCB and a MORS resistor has been added to the input stage due to the problem of generating a lot of heat.

As an alternative, if there is a device suitable for Energy Star in a small package size, please recommend it.

Please check. Thank you.

  • 0
    TI__Expert 6799 points

    Hey Grady, 

    The LM317M (TO-252) package is 67mm2. I would recommend switching to the LM2940-N or LM2941 in WSON package (16mm2). Another great options is the TPS7B86-Q1  in the SO PowerPAD package (19 mm2). These devices will be suited for specs provided above as well. Let me know if you have any further questions. 

    Thanks, 

    McKyla

  • 0 in reply to McKyla Beuttler
    Genius 4255 points

    Hi, McKyla

    Thank you for the reply.

    I have additional questions.

    The customer asked for a replacement for the small package of the LM317MKVURG3, but they said that they used a MORS resistor at the input stage because a lot of heat was generated even though the large package of TO-252 was used.

    In my opinion, even if you use a MORS resistor at the input stage, it will generate a lot of heat.

    The reason is the SPEC used by the customer: DC24V -> +5V, 500mA.
    According to this specification, the drop voltage is about +19V.

    In my opinion, if you use an LDO, it will generate a lot of heat, so it would not be suitable. Is that correct?

    Instead of LDO, I think it is right to recommend DC-DC (Buck).

    Are there any parts you would recommend?

    Please check.  Thank you.

  • 0 in reply to Grady Lee
    TI__Expert 6799 points

    Hello Grady,

    Yes, this will be about 9.5 W of power which will generate a substantial amount of heat using any LDO. There are different things that you can do to help reduce the heat, app note linked here: Thermal App note. We still would recommend using a buck converter to get down to 5V and then cleaning up the rail with an LDO. For the LDO I would recommend using the TPS7A94 or the TPS7A20 to clean the rail. 

    I will let the buck converter team respond on what they would recommend using. 

    Thanks, 

    McKyla

  • +1 in reply to McKyla Beuttler
    TI__Genius 14455 points

    Hi Grady

        TPS62175 is a device that can operate upto 28V Vinmax at 0.5A.

    https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=2C2A409F2A1DD402

    Here is a copy of the design in WEBENCH.

    Regards,

    Gerold