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TPS65130 w/ 5V Input and +/-12V Outputs - Further to existing post

EngH060
Intellectual 365 points
Other Parts Discussed in Thread: TPS65130

I have a customer interested in designing a +/-12 v supply with the TPS65130.  His available input voltage is 5 volts, and his projected load current is pretty small at +/- 5mA peak.  When he and I run through the inductor design equations on page 24 of the Sept 2004 data sheet, we get very large values for the inductors.  Positive inductor is in the vicinity of 620uH and the negative inductor is around 530uH.  These values seem out of line with what is recommended in the data sheet and we are concerned that the 65130 is not suitable for his application.  Can you confirm the 65130 will work ok here, and if not, can you recommend an alternative?

  • 0
    TI__Guru**** 165786 points

     

    Neil,

    Because the TPS65130 is internally compensated, you will need to use inductors within the recommended inductance range in the datasheet.  You should use the largest recommended inductor.  The key difference in operation between the larger inductance and the smaller, datasheet-recommended inductance is the transition point between continuous conduction mode and discontinuous conduction mode.  Any efficiency differences should be mitigated if you plan to use power save mode. 

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 365 points

    Jeff:  Thanks for this. I apprecate the guidence on using the inductors recommended within the data sheet.  Your answer implied that it would be fine to attempt to generate the outputs of interest with the TPS65130, but can I ask that you confirm this implicitly?  Sorry to belabor the point.

  • 0 in reply to EngH060
    TI__Guru 65170 points

    Hello Neil,

    TPS65130 is able to work with your specification even if the calculated inductors are way off from the recommended ones. The difference will be that you have a ripple current higher than 20% of your average current, but this is not a problem for the part. The part does not need a minimum output current to stay in regulation.

    If you want to be absolutely sure that everything is fine with this part, you could use the evaluation module to evaluate the voltages you want to use. You also could use the parts you want to use and evaluate them on the existing layout.

    Best regards,
    Brigitte