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TPS61500: Power management forum

cd feak
Prodigy 135 points
Part Number: TPS61500

Note i can supply direct to a TI app engineer by email ----- specific  pdfs of the 2 schematics when requested but will not post them on a public ti portal

Number: CS0315134 Contact: cd feak First name: cd Last name: feak Short description: not seeing drive capability with my design Phone: 16266428886 Email: cdfeak@psadvancedeng.com Company: azure medical technologies Company phone: Language: English State: Open Provide case details or comments: hi richard i am a bit stuck here

changed my design to 9 of the cree xpred 701 series 630nm parts from the original 5 of those parts.

www.mouser.com/.../XLampXPE-221789.pdf

was able to make the 5 series cree work just fine with 400mA as drive...and up to 7 of the same parts

now just cannot get the part to power 9 of these at anywhere near their rated optical output even with I drive set for 400mA----they are just real dimmed down with 9 of them series hooked now.

ATTACHED ARE THE ARRAY AND THE DRIVER PCBA SCHEMATICS

lipoly 3.7-4-2vdc 2400mA 1 c rive capability (its not the battery---i also directly hooked a dc 4v power supply thinking first maybe battery was straining to meet the 1A ---even though 400 is way below that 1A)

what might be wrong here?

have a good sumida inductor and a low dcr 3a schottkey

supposed to be a 40v switch --- the crees vF totals are not adding to 40v

operating no pwm---steady state=== yes a higher load on output but it seemed this part should handle ok

CD (Don) Feak
Azure
AMT Global (Calif C- Corp)
Technologist

626-642-8886 Office
626-281-9531 Fax

WhatsApp: c feak
WeChat : cdf62xke
SMS/Mobile +1 626 841 4856
LINE: cdfeak or cdfeakusa
Skype: cd feak or roadster62xke

cdfeak@azuremedtech.com
www.azuremedtech.com

On 3/22/2018 7:06 AM, support@ti.com wrote:
>
> Don,
>
> I am sorry that I could not call yesterday, but I have no company phone at my house.
>
> Please let me know if you have any further questions or comments.
>
> Regards,
>
>
>
> Richard Elmquist
> TI Applications Support
> Americas Customer Support Center
> 512-434-1560
>
>
>
> http://e2e.ti.com/
>

  • 0
    TI__Genius 13001 points

    Hi cd,

    The issue description is a little confusing. Could you please describe it simply and clearly? Thanks for your understanding!

    BR,

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 135 points

    simply put

    the tps61500 will not drive 400mA into 9 Cree XPE Red LEDS in series

    vF total is under the rated 40V tps switch...not a thermal issue at all.....just not enough current drive.

    will drive 7 (but not 8 or 9) of those leds in my current config --- but bogs way down and wont drive 9 crees

    i have the drive and array schematics in pdf.

    i could send to an email if you dont mind providing one to send to.

    Thank you for taking a look!

  • 0 in reply to cd feak
    TI__Genius 13001 points

    Hi cd,

    How about the input voltage? Since the minimum current limit is 3A, so low input will trigger current limit. Can you check it?

    BR.

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 135 points

    hi robin

    lipoly 2500mA 1c discharge rate 3.7-4.2v 

    battery Vin should not be an issue at all.

    Channels (#)1Vin (Min) (V)2.9Vin (Max) (V)18Switching frequency (Max) (kHz)2200Product typeInductiveLED current per channel (mA)400

    on my schematic i sent originally im not seeming to be outside of any of these parameters in the spec sheet

  • 0 in reply to cd feak
    TI__Genius 13001 points

    Hi cd,

    For 4V Vin, 40V Vout and 400mA Iout, the Iin could be up to 40Vx400mA/4V=4A, so it's possible to be above current limit. I think this is the root cause.

    BR,

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 135 points

    Forward voltage (@ 350 mA) - amber, red-orange, red, HE photo red V 2.1 2.5

    Forward voltage (@ 700 mA) - red-orange, red, HE photo red V 2.3

    actually these Vfs are off the Cree Datasheet  for 701series xpred leds im using

    at the max vf of 2.5Vdc --- 9 of these is 22.5Vdc and the supposed worst case at 25C for this is 2.25A

    so your number is off quite a bit 

    did you view the schematics i attached or not?

    can you?

    i need this to be checked to see what i might need to tweak --- to make this work --- else have to do something different. 

  • 0 in reply to cd feak
    TI__Genius 13001 points

    Hi cd,

    I will request friendship from you and then you can send me the schematic. Thanks!

    BR,

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 135 points

    so using the insert file with the little paperclip icon above method does NOT attach a pdf schematic file.

    these schematic pdfs are not large---about 250kb total size

  • 0 in reply to cd feak
    TI__Genius 13001 points

    Hi cd,

    According to your schematic, the resister divider consists of 120kOhm and 10kOhm resisters, so the OVP should be about 1.229Vx13=16V, which may be lower than 9 or 8 LEDs voltage in series. 

    BR,

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 135 points

    Haaaa!

    Completely overlooked by myself.

    And that, Robin is why you are a TI intellectual designated person!

    Thanks---should have been obvious to me but i have too many vectoring things going on to catch the detail that you did:)