Boost Converter Problem - Continuity Across Battery Connector

Discussion in 'The Projects Forum' started by laredo7mm, May 21, 2009.

  1. laredo7mm

    Thread Starter New Member

    May 21, 2009
    3
    0
    Hey all, new here and not very good at electronics so I was hoping you could help me out.

    I am trying to design and build a boost converter to provide a 5V output from a 3.7V nominal Li-Poly battery. The load will be about 1.5 amps. I am using a Maxim MAX1709 16 pin SOIC as the boost converter. I used DipTrace to draw the schematic and design the PCB. I then used the laser printer toner transfer method and etched my PCB.

    The problem is that after getting the components soldered to the board, and plugging in the battery, I have 0V for the output. I measured the voltage across the battery connecter and it was 0V. I disconnected the battery and checked for continuity across the battery connector and it showed continuity. So what I am thinking is that is causing my Li-Poly to kick into short circuit protection and shut down.

    I would appreciate it if you all could take a look at the attached pictures and let me know what I have done wrong. Thanks in advance.



    An Example Circuit from Maxim:
    [​IMG]



    My Schematic:
    [​IMG]


    My PCB Layout:
    [​IMG]
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If you want 1.5 Amps at 5V then the current drawn from the battery will be about 2 Amps.

    I don't think a 3.7V cellular phone battery can supply 2 Amps continuously.

    Do Li-Poly batteries have a built in overload protection? I didn't know that.
     
  3. laredo7mm

    Thread Starter New Member

    May 21, 2009
    3
    0
    The Li-Polt I have is a 2C battery with a capacity of 2000mah, so according to the specs, I can pull 4 amps from the battery. But the PCB on the battery limits it it 3A. The PCb on the battey also protects it from over charge and over drain.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Tell us the part number of the battery or a link to provide more information about it.

    What is more, check your PCB for a short circuit (solder splash or whatever).
     
  5. laredo7mm

    Thread Starter New Member

    May 21, 2009
    3
    0
    Here is the link to the battery I bought:

    http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4354

    I checked for jumpers and all of that. I didn't mention that this is my third board that I have made. The first one worked for a little bit, but then it stopped working. On the first two boards, I thought that maybe I shorted the output leads together when I was measuring for Vout and that is what caused my problems. But on this board I am just measuring from the connector contacts.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    It's your layout problem, it's causing parasitic capacitance and shorting out the IC or the battery
    Make the Voltage traces thicker and shorter.
    Rifaa
     
  7. hmms

    New Member

    Jul 7, 2009
    1
    0
    I have a very similiar problem designing a similiar circuit.I am Using the TPS61200 boost Converter IC. And using a 3.7V lipoly battery rated at 2800mAh Nominal Capacity with a Discharge Current rating of 2C. I have Configured the Chip for an output of around 3.3V ,and i will be loading the chip upto 500mA max.

    When the circuit is unloaded or has a light load of under 100mA,the circuit works fine. But if the load increases to around say 400-500mA the IC heats up and blows up,shorting the two battery terminals,Can you please suggest a good layout method,or some fool proof way to get the layout right???

    I asked on the TI forums too....and they too suggested that the layout was the issue.
    Here's the discussion over on TI forums.

    Please help...
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,650
    2,348
    Hello,

    I can NOT see any of your pictures in the first post.
    Please UPLOAD them to the forum as attachments.

    Bertus
     
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Boost converters draw huge peak currents on start up. One way around it is to have giant storage caps at the power in terminal that charge up from the battery before you turn on the boost converter.
     
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