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Negative input positive output non-isolated converter

A Kumar
Prodigy 215 points
Other Parts Discussed in Thread: LM2576, LM2587, LM2585, TPS61175, TPS55340

Dear Sirs,

Greeting for the day!!

I would like to convert the -15V input to +5V/2A output non-isolated topology, kindly suggest the TI IC part numbers which could be do this and schematic diagram, Please suggest me TI IC in through hole package i.e. TO-220 etc. 

Thanks & warm regards

Atul Mishra

Hyderabad, India

  • 0
    TI__Guru 72625 points

    Please see the attached app note; you may find it helpful.

    8032.snva740.pdf

  • 0 in reply to Frank De Stasi
    Prodigy 215 points

    Dear Sirs,

    Greeting for the day!!!

    we can used another IC such as LM2576 etc  instead of the LM2587 as recomdeded in application note SNVA740, if possible with another IC kindly give the IC names and relevant schematic . it would be more helpful to me.Ehat is major critria of IC which we could used for Negative input positive output non-isolated DC-DC Converter.

    Thanks & Regards

    Atul Mishra

  • 0 in reply to A Kumar
    TI__Guru 72625 points

    This type of topology requires the use of a boost regulator; the LM2576 is a buck.  Can you explain the term "Ehat" ?

    Thank you

  • 0 in reply to Frank De Stasi
    TI__Guru**** 191445 points
    I think he meant to type "What is the major criteria...".
  • 0 in reply to Frank De Stasi
    Prodigy 215 points
    Dear Mr. Frank De Stasi,
    Thank You very much,
    Greeting for the day!!!
    Could you please suggest the boost IC's part numbers except LM2587 which can support this configuration , Kindly share the schematic of the relevant Boost IC used for negative to positive buck boost converter for a such parameters
    Input- (-)15V DC
    Output- (+)5V DC/2A
    Load & Line regulation >1%
    Ripple>50mVp-p

    Regards
    Atul Mishra
    India
  • 0 in reply to JohnTucker
    Prodigy 215 points
    Dear Mr. John Tucker & Mr. Frank De Stasi
    Thank you sir

    sorry for drafting error, "Ehat" means "what is is major criteria of IC which we could used for Negative input positive output non-isolated DC-DC Converter." kindly explain

    Regards
    Atul Mishra
    India
  • 0 in reply to A Kumar
    TI__Guru 72625 points

    You will need a boost converter with a switch and input voltage of at least 17V = 12V + 5V.  The switch current limit should be at least 3A for a 2A load at 12V input.

    Devices such as the TPS61175, TPS55340, LM2585 should work.

    Keep in mind that this is not a common application, so you will need to test your design very carefully.  The best place to start is the app note that I sent you.

  • 0 in reply to Frank De Stasi
    Prodigy 215 points
    Dear Mr. Frank De Stasi,
    Greeting for the day!!!
    Please send the schematic of the DC-DC converter by using LM2585IC as per given spec.
    Input- (-)15V DC
    Output- (+)5V DC/2A
    Load & Line regulation >1%
    Ripple>50mVp-p.

    Thanks you very much in advance.

    Regards
    Atul Mishra
    Hyderabad, India
  • 0 in reply to A Kumar
    TI__Guru 72625 points

    You can use the same schematic for the LM2585 as with the LM2587.  Please be sure to test your design before commiting to production.

  • 0 in reply to Frank De Stasi
    Prodigy 215 points

    Dear Mr. Frank De Stasi,
    Greeting for the day!!!

    I am converting the negative voltage to positive voltage with same ground using the IC LM2587T-ADJ. I  have assembled the PCB as per the application note snva740.pdf. and triyng to achieve the given below specification

    Input- (-)15V DC
    Output- (+)5V DC/2A
    Load & Line regulation >1%
    Ripple>50mVp-p.

    While i am feeding the Input- (-)15V DC to IC LM2587T-ADJ at no load condition, its taking more than 3A input current and input voltage drop, its much larger than normal operation which shown the somewhat input  pins shorting but i checked input pins ok, is it internal shorting in IC happening by this configuration as per snva740.pdf., i changed the two ic but problem is still there. Kindly suggest to me fundamental of problem as well as relevant solution.

    many many thanks in advanced

    Regards

    Atul Mishra

    India

  • 0 in reply to A Kumar
    TI__Genius 16025 points
    Atul,

    How did you layout the board? Did you follow the guidelines on Page 7 and 8?

    Can you take a picture with your phone of your board and post it here?

    When you say you checked the input pins and they are ok, how did you test this?

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Prodigy 215 points
    Dear Mr. Anston,

    Greeting for the day!!!!

    I assembled the exact circuit as per application note snva740.pdf as given on page 2 as well as followed the Layout guideline as per given page 7 & 8.I checked the pin 5 & 3 for knowing the possibilities of the shorting through the multi meter continuity mode., but its ok only, Sir when i feed the (-)15V to PCB its draw more input current at without load condition. P lease help me sir or else kindly suggested to me another IC and circuits for given below specification.
    Input-(-)15V
    Output-(+5)V/2A


    Regards
    Atul Mishra
  • 0 in reply to A Kumar
    TI__Genius 16025 points
    Atul,

    We are milling a board to send to your location so you can populate it and evaluate this application.

    Without a picture of your layout, or waveforms, we cannot diagnose what problem you are seeing. It could be anything from excess solder shorting something out, to improper component placement.

    What is the reading on the multimeter continuity?

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    TI__Genius 16025 points
    Hi Atul,

    Can you send us your complete mailing address along with Contact information and phone number?

    Please send this info to anston ['At'] ti ['dot'] com.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Prodigy 215 points

    Dear Sirs,

    Greeting for the day!!!

    I have come across to many problem when i converter negative voltage to positive voltage with common ground using IC LM2587T-ADJ through the circuits suggested in application note SNVA740.pdf, Now i would like to simulate IC LM2587T-ADJ at circuit which suggested for negative to positive voltage converter as per app. note SNVA740.pdf in Pspice ,LTspice, any TI simulation software etc. Sir it might be  Pspice transient model is not available in TI of IC LM2587T-ADJ, Kindly guide us how to generate the Pspice model of IC LM2587T-ADJ, or any other best way to simulate the IC LM2587T-ADJ for negative to positive conversion as per circuit suggested.  

    Many many thank you.

    Warm Regards

    Atul Mishra

    India

  • 0 in reply to A Kumar
    TI__Genius 16025 points
    Hi Atul,

    We don't have a model for this part.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    TI__Genius 16025 points
    The board has shipped to you. I will provide tracking information tomorrow.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Prodigy 215 points
    Dear Mr. Anstom Sir,

    Thanks for your cooperation.

    Sir could i simulate IC LM2587CT-ADJ for negative to positive conversion as per suggested ckt in application note SNVA740.pdf. Sir my another request to you kindly provide us samples of IC LM2587T-ADJ. It would be more helpful to me for diagnose the actual problem. Please do the needful.

    With warm regards
    Atul Mishra
  • 0 in reply to A Kumar
    Prodigy 215 points
    Dear Mr. Anstom Sir,

    Please let me know is it simulation possible of IC LM2587CT-ADJ for negative to positive conversion as per suggested ckt in application note SNVA740.pdf in WEBENCH.

    Thank you
  • 0 in reply to A Kumar
    TI__Genius 16025 points
    I Sent the IC samples.. You should receive an email shortly
  • 0 in reply to A Kumar
    TI__Genius 16025 points
    Yes try Webench
  • 0 in reply to Anston Lobo
    Prodigy 215 points

    Thank you Mr. Anston.

    With warm regards

    Atul Mshra

  • 0 in reply to Anston Lobo
    Prodigy 100 points
    Dear Mr. Anston Lobo,

    Good day and wishes !!!

    Boss i am trying to convert negative to positive voltage using LM2587T-ADJ on general purpose PCB board using lot of wires for making connections, is it correct way to testing of circuit temporary basis instead of mount on proper fabricated PCB.what is the drawback of general purpose PCB mounting rather then correct mounting on relevant PCB.IC could be more heated on no load at general purpose board or not as compare to relevant PCB and why? ???

    Thanks & Warm Regards
    Atul Mishra
  • 0 in reply to Atul Kumar20
    TI__Genius 16025 points
    Atul,

    It is never a good idea to just use wires to route a PCB containing a switching DC-DC regulator. The parasitics from long wires, even short wires would make the regulator unstable.

    I highly recommend layout on a pcb with proper fabrication.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Prodigy 100 points

    Dear Mr. Anston,

    Greeting for the day!!!

    I received the assembled PCB board and samples of the LM2587T-ADJ, Qty- 15 nos sent by you.

    Many many thank you for this support.

    1. I tested the assembled PCB board, voltage is converting -12V to +5V@1A  with common ground , output voltage is also constant when varies the input 4V-20V, sir you sent assembled the PCB as per application note for negative to positive conversion `SNVA740.But  i got the output ripple 288mV P-P with this PCB ,my input is regulated DC voltage.My requirement is output ripple >50mVp-p. how to achieved this specification in assembled PCB sent by you ,any extra filter required at output side ? Kindly guide me.

    2. Boss i assembled the LM2587T-ADJ IC on my own designed bare board PCB and mounted all components by same value and location as suggested in application SNVA740 for converting -12V to +5V@1A , when gives input -12V output +5V is coming but output voltage is not stable it means when i increase the input voltage -12V to -13V converter output is decreasing like 3.1V further increase the input , output voltage is decreasing  and goes to zero whereas when input voltage is decrease from the -12V to -10V,-8V,-5V converter output voltage is increasing 5.2V,5.3V,5.4V respectively. It means my converter voltage is not stable as well as unregulated. Whereas in assembled PCB sent by you i got stable and regulated output. what i am doing wrong , i assembled and prepare PCB as per application note. 

    Kindly guide me.

    Thanks & warm regards

    Atul Mishra

    Hyderabad, India

  • 0 in reply to Atul Kumar20
    TI__Genius 16025 points
    Hi Atul,

    Try adding an LC filter at the output, with a 10uH inductor with a DCR of 20mOhms or less and capacitor of 2uF with an ESR of 50mOhm.

    Depending on the DCR, the circuit's load regulation will be affected. Higher the DCR, higher the drop on the output, but better damping.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Prodigy 100 points

    Dear Mr. Anston Sir,

    Greeting for the day!!!

    I putted the L-C filter across the output L=10uH, DCR=8 mohm, C=2uF, ESR=5mohm for the output ripple reduction purpose but still getting ripple 300mVp-p at 1A load but when i increase the value of L=1mH and C=2uF  converter output ripple reduced to 20mVp-p at 1A load  which is under my specification. Please let me know as you suggested the value of an inductor should be 10uH , is that any problem with converter health if putted L=1mH at L-C filter in output side rather then L=10uH? or any other also method  to control the output ripple of the converter. 

    I am measuring the ripple by short loop the probe of oscilloscope with 47uf capacitor across it, any other better method to ripple measurement is there.

    Thanks & Warm regards

    Atul Mishra

  • 0 in reply to Atul Kumar20
    TI__Genius 16025 points
    Atul,

    The values I provided were approximate. It is very likely that the values you selected will work.
    Apply a load transient on the output and check for any instabilities, I don't expect there to be any, but this will be a sanity check.

    Your ripple measurement technique is sufficient.

    -Anston
  • 0 in reply to Anston Lobo
    Prodigy 100 points
    Dear sir,

    How to measure an inductor current ,you given the test point in PCB for measure the Switching waveform but how to measure the inductor current waveform by CRO, at which point i have to connect the probes of the CRO. sorry for this much questions.

    Many many thank you.

    Regards
    Atul Mishra
  • 0 in reply to Atul Kumar20
    TI__Guru**** 191445 points
    To measure inductor current, I typically un solder one end of the inductor and install a short wire loop between the inductor lead and the PCB pad. I use a clamp on current probe around the wire to measure current. works best on the non-switching side of the inductor.
  • 0 in reply to JohnTucker
    Prodigy 100 points

    Thank you very much Mr. Anston & Mr. John Tucker.

    Regards

    Atul Mishra

    Hyderabad, India

  • 0 in reply to JohnTucker
    Prodigy 100 points
    Dear Mr. Anston, Mr. Frank & Mr. John.

    Greeting for the day!!!

    I am also going to design the boost converter as given below specification.

    Input : 3.3V (3.2-3.4V)

    Output: 5V@2A

    Line & Load Regulation :1% of the output voltage.

    Ripple>50mVp-p

    Efficiency> 85%

    IC operating temp. should be -40 dec C to +120 deg C.

    Size of the solution : Small as possible.

    Please suggested the suitable IC's part no. and schematic for this solution.



    Thanks & warm regards

    Atul Mishra

    Hyderabad, India
  • 0 in reply to Atul Kumar20
    TI__Genius 16025 points
    Atul,

    Using Webench will help you to do this. If you have any question let us know. Attached is a recommended design.

    webench.ti.com/.../SDP.cgi

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Prodigy 215 points
    Dear Mr. Anston, Mr. John

    Greeting for the day!!!

    I am going to design the DC-DC Converter based on the Forward topology on below mentioned specifications. Kindly suggest the suitable IC and electrical schematic as well as Components BOM.

    I would like to simulate this schematic on Pspice/LTspice prior to fabricate the PCB and procurement the components ,so please suggest that IC and schematic which have the Pspice model or able to simulate.

    Input: 18-36VDC(Nominal 28V)

    DC Output(Floating): +15V/1.5A & -15V/1.5V.

    Line, Load & Temp. Regulation :1% of the output.

    Ripple & Noise: Less than 50mVp-p

    Topology : Forward ( or else kindly suggested)

    Switching Frequency: 250kHz

    Efficiency: Greater than 75%

    Isolation : 200V between input & output, input & case, output & case.
    Input DC Protection: Reverse Polarity, Under and Over Voltage Protection with auto recovery.
    Output DC Protection :Electronic Over-Voltage Protection , Current Limiting – Continuous protection for unlimited time with auto recovery, Indefinite short circuit protection with auto recovery.
    Over Temperature Protection: Shutdown at base plate temp of +105°C (±5°C) Automatic recovery at base plate temp lower than 95°C (±5°C)

    EMI/RFI :Built-in Input & Output Filters as per MIL-STD-461E.
    Environmental:Meets or exceeds requirement of MIL-STD-810G
    Signals:

    1. Inhibit: TTL "1" or open to turn ON the power supply, TTL "0" to turn OFF the power supply.

    2. Sync IN : To allow the power supply frequency to sync with system frequency.

    Kindly suggest the appropriate data.



    Many many thank you in advance.



    With Warm Regards

    Atul Mishra

    Hyderabad, India
  • 0 in reply to A Kumar
    TI__Guru**** 191445 points

    I'm going to make this a new post and put it into the isolated dc/dc forum.