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TPS61107 startup under load

Other Parts Discussed in Thread: TPS60120, TPS61107, TPS60140

I am trying to convert my current application with TPS60120 (200mA max) to TPS61107 to get about 280mA from two cell Ni-MH batteries (~2.4V)

TPS 61107 starts just fine at 3.3V and 140mA load on main output, at this point and can add another 140mA and get stable 3.3V

With any larger startup load 150mA+ I can get on start up only 2.1V

Any ideas why? Does it have anything to do with SKIPEN input that connected to VBAT?

I have a simple test board with 10uH inductor, input cap 22uF ceramic, output caps 2.2uF ceramic and 100uF tantalum

Thanks 

  • Some boost converters don't start up well into resistive loads.  This problem is typically only seen in the lab with resistive loads or an electronic load.  Real system loads act differently and don't cause problems.  If these parts didn't work well in real world applications, TI would not be able to sell them.  I have found that starting up into a lower load and then applying full load works well in a lab environment.  THe other option is to use your actual system as the load.  Personally, I would use one of TI's newer IC for this function.  They are smaller and more efficient, plus they use smaller cheaper external components.  TI has a good selection tool to pick a part for this function.  Go to www.ti.com, click on Power Management on the lower left side of the page.  The selection tool will provide many potential ICs.  I have used this often and it works well.

  • Michael,

    I did not try it with real application, this will happen next week, I just have a simple board with inductor and 3 capacitors

    In our current  application I have no problem to cascade loads: Microcontroller stats first, and if power is good, then I will turn on LCD backlight and Ethernet controller.
    Without backlight I am sucsessfully running this application on TPS60120 while LCD uses separate 5V source from TPS60140. New design will be using 3.3V LCD, but TPS60120 does not have enough power to run an additional 60mA backlight needs. That is why we are trying to move to TPS6110x and use it as the only source.

    I understand TI has many choices, but 6110x is the only one I know that has pushbutton Enable input the will eliminate few external components we have for this feature. If you know other ICs with functionality similar to PBEN, then let me know please.