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TPS61165 not working

aviad yeshaya
Prodigy 70 points
Other Parts Discussed in Thread: TPS61165

 hi

 

I got my first prototypes of the PCB based on the TI TPS61165 led driver. SOT-23 package - hand soldered

For some reason that are not clear to me now it's not working as expected do I want need some assistance.

Attached is the electrical scheme only R3 is connected and R4 is open ( used for future PWM control)

My LCD operates with 20mA current and 19VDC and when I plug it in the TPS61165 doesn't work. No switching is observed.

I checked of course that everything is connected where its suppose to and the power consumption is indeed 20mA everything was supposed to work but for some reason it doesn't.

when i feed the LCD from a lab power supply directly 19V i can see it works and consumes 20mA as expected.

 

Regards 

  • 0
    Prodigy 70 points

    hi again

    i replaced the TPS61165 with another one and now the LCD is working but the SW pin shows the following waveform any thoughts?

  • 0 in reply to aviad yeshaya
    TI__Guru**** 166176 points

    The waveform above is the boost converter running in discontinuous mode (DCM).  In that mode, the inductor current ramps down to zero.  The oscillations (usually called ringing) that you see are normal and are simply caused by the inductor dumping its excess energy.  While it is acceptable for the IC to run in this mode, it usually is not the most efficient mode.  Continuous mode is usually more efficient.  What is your input voltage?  With it,  I can help you increase the inductor's inductance until the IC runs in CCM.  Note that when you start dimming, you will likely eventually hit DCM anyway.

    Your schematic appears okay.  Perhaps a bad solder joint on the CTRL pin of the first IC prevented it from turning on?

  • 0 in reply to Jeff F
    Prodigy 70 points

    hi

    thanks for your answer.

    I am using 12VDC as Input and my LCD requires 19VDC. my Inductor as you could see is 10uH.

    i never saw the ringing in other DC/DC converters that i used to work with. the output voltage is steady but the DCM won't damage the tps61165? how can i stop the ringing and operate in Continuous Mode?

    regards 

  • 0 in reply to aviad yeshaya
    TI__Guru**** 166176 points

    DCM is perfectly acceptable mode for operation.  In fact, given your high input voltage, you will have to increase your inductor > 180uH (as I explain below) to ensure CCM mode.   An inductor with such large inductance will have higher DC resistance than a smaller inductor and so that might kill any efficiency gains from running in CCM.

    Using d/s equation 5 and assuming efficiency of 90% (a low estimate), I get Iin_DC=35mA.  Choose Ip=60% of Iin_DC = 21mA.  Rearrange equation 3 to solve for L for Ip=21mA and you get 182uH.

  • 0 in reply to Jeff F
    Prodigy 160 points

    Hi,

    We are using TPS61165DBVR in our design for a LCD back light. We are using control pin as enable ( No brightness control) and it is 3.3V from a IO of a processor. Input voltage is 5V. I have not seen any switching pulse in pin 3. Here is my circuit. I have replace two new Chipset. But so far no result achieved.  Please share your comment. 

    .  

    Thanks in advance,

    Vijay

  • 0 in reply to Vijay Anand
    TI__Prodigy 520 points

    Hi Vijay,

    Could you tell me about your output voltage? 

  • 0 in reply to Ming Dai
    Prodigy 160 points

    Hi Ming Dai,

    The required output voltage for us is 10V.

    With Regards,

    Vijay

  • 0 in reply to Vijay Anand
    TI__Prodigy 520 points

    Hi Vijay,

    It seems strange, so could you show me some waveforms? I'd like to see the waveforms of Vin, Vcntrl, Vsw and Vo  in start up procedure if you have a four channel scope.

  • 0 in reply to Ming Dai
    Prodigy 160 points

    Hi Ming Dai,

    Yes it is strange.  Finally it worked by replacing one more new IC. Thank you for your support.

    With Regards,

    Vijay