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LM317: I need assistance identifying better replacements for LM317/337 series devices; needs below

Grant Lenahan
Prodigy 10 points
Part Number: LM317
Other Parts Discussed in Thread: LM2991, LM337, , LM350-N, LM350A, TPS7A33, TPS7A47, LM2941, LM2941C, TPS7A39

Hello,

This is my first post. Ignore anything in my profile, i have overall archietcture and design responsibility across hardware and software for our products, which are often building blocks. These modules/designs are used in more than one sector, so the characterization form is very misleading.

I have several related designs nearing completion.  All are powered by a series of power supply stages. The middle stage uses a modified commercial regulator, 337/317 pairs, but with a number of additions for better performance.  I am seeking more modern designs that are are lower noise specifically in two ways:

1. lower board spectrum noise. That said I can manage most of this with an LC after the regulator

2. much better power supply (120 Hz and overtones) ripple rejection.  Sadly, even with a rippled rejection capacitor and generous caps at the input and output terminals, i am getting only about a 200X reduction , which in my world is 46 dB not the 60-70dB listed int he datasheet.  Possibly i need to know more about what test configuration the datasheet makes this claim for, but its largely irrelevant since the performance is not great. Draw is ~ 250-300 mA, mostly continuous (mostly class-A operation) at + and - 15Vdc.

Requirements:

Linear operation

Input voltage to 30V

Adjustable output to at least 18V - more preferred

both +V and -V complementary pairs (e.g.: 317,337)

1A output continuous (rarely seen)

3W continuous with heat sink (rarely seen)

Through hole version available strongly preferred for prototype/early test production with move immediately to SMT for volume

(best package is TO-220)

I did a search and found nothing obvious. I did see the TPS 7A470 series but they are -- if i read properly -- 20 pin, SMT, and needlessly complex. I really just want an improved, or focused on noise, 317/337.

I hope to avoid building a discrete solution myself - i moved away from that to gain simplicity, protection and size.  But right now its planB since i know it works.

Maybe i need to go over to LT/AD?

Grant

  • 0
    TI__Expert 5136 points

    Hello Grant,

    For LM317, the only option I see is LM350 series. For LM337, the option I see is LM2991 in our portfolio using TO-220. Below is the comparison table, please let us know if you have any questions.

      LM317 LM350-N LM350A LM337 LM2991
    AEC Q100 NO NO NO NO NO
    Output Options Adjustable Output Adjustable Output Adjustable Output Adjustable Output, Negative Output Adjustable Output, Negative Output
    Iout (Max) (A) 1.5 3 3 1.5 1
    Vin (Max) (V) 40 35 35 -3 0.3
    Vin (Min) (V) 3 4.2 4.2 -40 -26
    Vout (Max) (V) 37 32 32 -1.2 -3
    Vout (Min) (V) 1.25 1.25 1.25 -37 -24
    Fixed Output Options (V) - - - - -
    Enable NO NO NO NO YES
    Power Good NO NO NO NO NO
    Output Capacitor Type Non-Ceramic Non-Ceramic - Non-Ceramic Non-Ceramic
    PSRR @ 100KHz (dB) 38 40 40 19 22
    Noise (uVrms) 38 13 13 1110 200
    Accuracy (%) 5 3 1.8 2.4 5
    Vdo (Typ) (mV) 2000 2300 2300 2000 600
    Iq (Typ) (mA) 5 0.05 0.05 1.5 0.7
    Thermal Resistance θJA (°C/W) 24 35 35 23 28
    Min Package Area (mm2) 45.5 46.5328 46.5328 66.726 86.0552
    Package Type DDPAK/TO-263, SOT-223, TO-220, TO-220 TO-220 TO-220 DDPAK/TO-263, TO-220, TO-252 DDPAK/TO-263, TO-220, TO-220

    Thanks,

    Prakash L

  • 0 in reply to Prakash Lakhit
    Prodigy 10 points

    Hi Prakash, but I'm confused by a few things.  First, the PSRR my biggest concern, is roughly the same -- or am i misreading? 

    next i see for the LM2991 i see a max Vout of -3V. or are you ignoring he magnitude and referring only to the sign. Somewhat odd but maybe that explain it.

    Do i have better options if i accept that i cannot have TO-220/THT? 

    Thanks,

    Grant

  • 0 in reply to Grant Lenahan
    TI__Expert 5136 points

    Grant,

    Yes, not a great improvement in PSRR. Also, the sign is the reason for the confusion like you mentioned. If you can live with a max Vin of 26V, then I suggest that you try LM241C and LM2941 devices. If that doesn't work, then your best bet is TPS7A47 series for positive and TPS7A33 series for negative with 20 pins. Hope this helps, we are working on devices that might fit this portfolio in the future. However, don't think they are planned in anything less than 8 pins.

      LM317 LM2941 LM337 LM2941C
    AEC Q100 NO NO NO NO
    Output Options Adjustable Output Adjustable Output Adjustable Output, Negative Output Adjustable Output
    Iout (Max) (A) 1.5 1 1.5 1
    Vin (Max) (V) 40 26 -3 26
    Vin (Min) (V) 3 6 -40 -15
    Vout (Max) (V) 37 20 -1.2 20
    Vout (Min) (V) 1.25 5 -37 5
    Fixed Output Options (V) - - - -
    Enable NO YES NO YES
    Power Good NO NO NO NO
    Output Capacitor Type Non-Ceramic Non-Ceramic Non-Ceramic Non-Ceramic
    PSRR @ 100KHz (dB) 38 67 19 67
    Noise (uVrms) 38 600 1110 38
    Accuracy (%) 5 5 2.4 2.8
    Vdo (Typ) (mV) 2000 500 2000 500
    Iq (Typ) (mA) 5 10 1.5 10
    Thermal Resistance θJA (°C/W) 24 41 23 32
    Min Package Area (mm2) 45.5 16 66.726 86.0552
    Package Type DDPAK/TO-263, SOT-223, TO-220, TO-220 DDPAK/TO-263, TO-220, TO-220, WSON DDPAK/TO-263, TO-220, TO-252 DDPAK/TO-263, TO-220, TO-220

    Thanks,

    Prakash L

  • 0 in reply to Prakash Lakhit
    Prodigy 10 points

    thank you helpful, and your follow-up (below) is even more helpful (not entirely what i hoped to hear, but helpful!) :-)

    Strangely i cannot "reply" to that one.

    One last request since replacements are apparently complicated:  can you provide links to any documents (aside from the datasheet) on how to get better performance out of the 317/337 pairs?

    TIA,

    Grant

  • 0 in reply to Grant Lenahan
    TI__Expert 5136 points

    Grant,

    Checking with our applications team, will get back to you as soon as I hear from them.

    Thanks,

    Prakash L

  • 0 in reply to Prakash Lakhit
    Prodigy 10 points

    Thanks Prakash!   My biggest concern, since LC will effectively filter much hash, is power supply ripple and its overtones, so 120, 240, 480 Hz....  the nice thing about improving the 317/37 performance is that they are so widely available, and in essentially matched complements.

    Grant

  • 0 in reply to Grant Lenahan
    TI__Expert 5136 points

    Grant,

    I am assigning this to our apps team. Also, they would like to know if you could share your circuit schematics or any other details.


    Thanks,

    Prakash L

  • 0 in reply to Prakash Lakhit
    Prodigy 10 points

    Thank you for asking!  I appreciate that someone is taking this seriously.

    Since I am developing a family of modules and building blocks, being specific is difficult; there is no one final schematic. But i will try. Note i listed some of the most important characteristics in my initial request.

    in all cases the circuits are driven by a common raw supply, shielded from the low-noise circuitry.  That has independent, PCB mounted transformers for digital (noisy) and analog (clean) circuits, with independent grounds. The grounds are linked by 220 ohms in series with 2mH to tie the grounds to similar potential, but isolate noise.  This is also common practice in all mixed chips (including your own DACs).

    The raw supplies have the following topology, sized per the load at minimum 200% sizing:

    1. transformer
    2. bridge rectifier
    3. RC with ~ 5-50 ohms and 1000 - 2200 uF

    Followed by a common regulator
    4. Capacitance at input to regulators - 4700-2200, , with 0.1 film bypass
    5. LM317/337 with 10-100uF filtering the adj pin; heatsink as needed for <150F (not C), R1 220-500 ohms
    6. 1000-2200uF immediately after with ~0.47 film bypass
    7. if possible, series inductor < 1 ohm o control hash/noise

    Followed by a set of building blocks in different combinations, each with its own local electrolytic filtering and film bypass on each rail

    nearly everything is split-symmetrical rails (e.g.: minus and plus 15V)

    Digital supplies are not an issue

    Total draw never exceeds 350mA; regulators are 1.5A rated

    + rail alwasy draws more due to presence of buffers from +5V to ground and +15V to ground

    Loads  primarily operate class-A , but some have variable draw

    Gain of circuits varies greatly from V0/Vin <1 to Vo/Vin > 1500X (64-65 dB gain)

    It is primarily the circuits with 65 dB on gain that are presenting the challenge, as i presume you appreciate.

    Clearly my PSRR is not as good as i hoped, btu the low noise front ends are all differential and ought to have at least an extra 12-18dB PSRR

    These are used in professional instrumentation and audio signal processing, or so they are intended. Right now they are hum generators. with < 46 dB overall SNR at 1500X gain

    I am looking at quieter/less sensitive circuit typologies but i have also tested that a "perfect" power supply eliminates the problem. Maybe i mis-read the datasheet but the 317 claims something like 70 dB ripple rejection. I am seeing less than 45 dB, sometimes much less. Its the difference between awesome and flawed.

    TIA

  • 0 in reply to Grant Lenahan
    TI__Genius 12930 points

    Hello,

             I am looking into this, I will get back to you on Tuesday (09/07, after the long weekend) at the latest. Thanks!

    Regards,

    Srikanth

  • 0 in reply to Srikanth Lolla Venkata
    TI__Genius 12930 points

    Hi Grant,

                   Regarding the PSRR, may I ask what your frequency range of interest is? Beyond 10KHz, it is difficult to get more than 50dB of PSRR from LM337. If the TPS7A47 and TPS7A33 pair does not work for you, could you consider TPS7A39? It has both, positive and negative LDO in a package. It satisfies your input voltage and output voltage range and has very good PSRR performance over frequency. Perhaps the load current is a drawback. LM317/337 devices are fairly old devices, as a result we, unfortunately, do not have documentation on using them as a pair. Thanks!

    Regards,

    Srikanth 

  • 0 in reply to Srikanth Lolla Venkata
    Prodigy 10 points

    Hi and thank you.  I will look at the pair of devices suggested.  My noise issues are primarily low frequency (60 Hz and several overtones) - as i noted, i can handle higher frequencies with an LC segment more effectively.  TIA,  Grant

  • 0 in reply to Grant Lenahan
    TI__Genius 12930 points

    Hello,

             Hope the devices (TPS7A47-TPS7A33/TPS7A39) will work out for you. Thanks!

    Regards,

    Srikanth

     

  • 0 in reply to Srikanth Lolla Venkata
    Prodigy 10 points

    One is not available in a THT part -- making evaluation and testing difficult especially with existing prototype boards... so while they may be useful in future production, i am still looking for a better solution, and the advice on how to best achieve my goals with the known working parts, the old, obsolete, 317/337 (which really need a like for like improvement!)

  • 0 in reply to Grant Lenahan
    TI__Genius 12930 points

    Hi Grant,

                   At this point we cant offer an alternative solution apart from the parts already discussed above. If TPS7A47-TPS7A33/TPS7A39 do not work for you, then LM317/LM337 pair is the only option. I am curious about the setup you used to make the PSRR measurements. Please find attached an App note from Pico Test that describes our setup and how we make PSRR measurements. Their App note in fact makes use of LM317 to describe the methodology. Please also find attached an image showing PSRR measurements of LM337 at various load currents using this method. As long as sufficient head room is provided (~3V for example), for 350mA of load current, both these devices should be capable of providing ~60dB of PSRR at frequencies less than 1KHz (this can be seen in the attached documents). We are working on refreshing the design of these devices, but it will be at least another year before the new devices hit the market. Thanks!

    Regards,

    Srikanth

     Picotest App Note PSRR Measurement.pdf

  • 0 in reply to Srikanth Lolla Venkata
    TI__Genius 12930 points

    Hello Grant,

                       If the output current requirement is flexible and less than 150mA, TPS7A49-TPS7A30 or TPS7A49-TPS7A34 pairs could be options you could look at. They come in 8 pin DGN packages. Thanks!

    Regards,

    Srikanth

  • 0 in reply to Grant Lenahan
    Prodigy 10 points

    The dual part, TPS7A39, looks very interesting.  It does not have sufficient current for the entire +/- 15V draw, but could work well on a single board.  Is here any kind of adapter PCB that would allow me to test a couple units on existing, THT, hand-stuffed boards?  There's no way i can hand add that tiny, multi-pin part.  TIA, Grant

  • 0 in reply to Grant Lenahan
    TI__Genius 12930 points

    Hello Grant,

                       At this point, unfortunately, we don't have any adapter PCB boards that we can offer. We have a dedicated Evaluation Board for this device, to test and study it. Thanks!

    Regards,

    Srikanth

  • 0 in reply to Srikanth Lolla Venkata
    Prodigy 10 points

    is that this:?

    https://www.digikey.com/en/products/detail/texas-instruments/TPS7A39EVM-865/8106159

    Which is pretty much what i'm looking for - although it seems pretty complicated and (ok, its relative) costly for what I need.  I just found this references in the documentation.  Are you saying you have similar for the other parts too?  Remember my problem: i need to test these before i use them.  I cant do it by hand. Idealy i'd like to do early production with larger THT, but compromises have to be made ( in the TI product line anyway, less so in others i'll note)

    In full production SMT is no only OK, its preferred.  But i'm not there yet.

    Grant

  • 0 in reply to Grant Lenahan
    TI__Genius 12930 points

    Hello Grant,

                       Yes, the link you provided is the Evaluation Module for TPS7A39. Unless they are very old devices, we have dedicated evaluation boards for almost all of our parts. We recommend the use of these boards for your verification and testing purposes. Thanks!

    Regards,

    Srikanth

  • 0 in reply to Srikanth Lolla Venkata
    Prodigy 10 points

    Do you offer them as samples?

    Also, what is the efficacy of using two three-terminal regulators (78xx, 79xx, 317, 337...) in tandem.  Is the ripple reduction and PSRR effectively multiplicative (which, if the reference is incoming noise, it ought to be)?

    i realize the inherent/internal noise contribution may not be improved much if at all.

    TIA

  • 0 in reply to Grant Lenahan
    TI__Genius 12930 points

    Hello Grant,

                       TPS7A39 samples can be requested from the TI store at no charge, if they are in stock. The Evaluation Modules (EVM) will however need to be purchased at TI store. Yes, if the regulators are used in tandem then the ripple reduction (PSRR) is multiplicative, in that each stage will help successively reduce the ripple. Thanks!

    Regards,

    Srikanth