Connect with us

Constant off time mode possible for LED IC?

Discussion in 'LEDs and Optoelectronics' started by eem2am, Nov 21, 2012.

Scroll to continue with content
  1. eem2am

    eem2am

    422
    0
    Aug 3, 2009
    Hello,

    I wish to use the Supetex HV9910B LED driver in constant off time mode.

    Supertex HV9910B LED driver IC:
    http://www.supertex.com/pdf/datasheets/HV9910B.pdf

    ....The datasheet says constant off time is achieved by connecting the RT resistor to the FET gate driver, instead of to ground.

    However, the MXHV9910 is clearly EXACTLY the same part, and yet this constant off time mode is not advertised for this version of the chip....

    Clare MXHV9910 LED driver IC.
    http://www.clare.com/home/pdfs.nsf/0/713EA18902B59CCF85257566004FAD55/$file/MXHV9910.pdf



    .....So, as you can see, these two IC's are one and the same, so why is the Supertex version offering constant off time mode, but not the clare.com version.?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,517
    2,651
    Nov 17, 2011
    Well, it is "clearly not EXACTLY the same part". Note the "B" in the part number and the obvious difference in constant off time mode.

    This is not rare in the world of electronics: rather subtle differences only marked by an unobtrusive appendix to the part number.

    If you'r in doubt, contact the manufacturer.

    Harald
     
  3. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    In addition to what Harald said they are different brands of said chip, just like any chip there is going to be variances from manufacture to manufacture... Just look at the wide variety of 555 timer chips, specs all over the place, generally a universal swap out but not always if you are depending on a spec of one particular brand...

    End of day contact said manufactures and inquire or get samples and test...
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    From the first page of the HV9910B datasheet: "Enhanced drop-in replacement for HV9910"

    So you would expect that the HV9910 lacks features compared to the HV9910B.
     
  5. eem2am

    eem2am

    422
    0
    Aug 3, 2009
    The block diagrams for HV9910B and HV9910 are exactly the same......i dont see how one can be constant-off-time capable and the other not.

    The only difference between the HV9910B and the HV9910 is the fact that on page 5 of the HV9910B datasheet it states that the HV9910B has faster internal comparators than the HV9910.

    The block diagrams being the same is surely the give away here?........they are so similar, that they must both be constant off time mode capable, or both *not* constant off time mode capable....do you agree?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    No.

    There are 2 options:

    1) The original part works like the new part, however nobody told you about this useful behaviour. The new part is not really enhanced; it's all just a ploy by the manufacturer.

    2) The new chip is enhanced (just like it says in the documentation)

    There is no reason that what's inside those blocks is exactly the same.
     
  7. eem2am

    eem2am

    422
    0
    Aug 3, 2009
    The "blocks" are comparators, logic gates or flip flops.....there aren't too many variations in these items as regards behaviours in a PWM controller.....i think your first statement that the HV9910 probably did C.O.T. too is probably correct......

    ...unless they inverted the logic in the oscillator block.....so that the gate going low restarts the oscillator in HV9910B, but in HV9910 its the other way round......I have emailed supertex and hope for a reply, though am never lucky with semiconductor co's
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    11,517
    2,651
    Nov 17, 2011
    A block diagram is a block diagram is a block diagram...

    It showns the architecture of the chip in a general way without claiming to be complete.
     
  9. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Yeah what he said, the block diagram is not a complete circuit schematic or a complete layout of the die it's simply a basic flowchart of function... To keep using it as the basis for the chips being 'identical' is a very slippery slope that you will likely fail to navigate successfully...

    But, on the other hand f you want to keep insisting they are the same, why bother asking in the first place?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    Look, it *might* work, but it also may be unstable. The "B" variant is clearly different (unless you think they're lying to you).

    Give it a try, see what happens.

    Even if it does work, I would not use the original part that way.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-