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TPS65130 w/ 5V Input and +/-12V Outputs

George Ioakimedes
Genius 4950 points
Other Parts Discussed in Thread: TPS65131

We have an application that seems to be right in-between the specs of the 65130 and 65131. As stated in the subject we'll have a 5V input (coming from USB) and will be generating +/-12V outputs. Our peak current draws might be up to 150mA. There are plenty of load graphs in the datasheet but they don't quite show our conditions for the 65130.

Does anyone happen to have any data that would show if we would be OK with the 65130 and can save a little money? Availability isn't great on these parts so we wanted to place an order while we finished our design. The good news is that both parts seem to be drop in replacements so one design will handle either part.

Any feedback would be appreciated.

Thanks,

George

  • 0
    TI__Guru**** 151420 points

    From Figure 3 in the datasheet, 150 mA @ -10V is about all you can expect at 5V in.  So, at -12V out, the maximum output current would be lower.  Looking at equation 4 on page 24, ILN (maximum peak current, which should be less then the minimum value of the switch current limit of 700 mA) is 797 mA @ 5V in.  So, at 5V in, you are over the current limit of the 130.  The TPS65131 is required for this design.

    Also consider the tolerance on that 5V input.  For USB, it could very well be 4.75V, at which point the peak current is higher than 797 mA.  I would also point out that you are exceeding the 500 mA rating of a single USB port.

    The ICs are pin to pin compatible, so you could always do your testing with the 131 and determine exactly what your peak load current is--is it 150 mA or more like 130mA?  You could then drop down to the 130 for production, if your currents allow it.

  • 0 in reply to Chris Glaser
    Genius 4950 points

    Hi Chris:

    Thanks for your quick reply. The 150mA peak currents would really only be short bursts of up to 150mA (possibly lower) and a typical current draw of ~50mA. Your point about the 500mA maximum current of USB but I hadn't done a design boosting from USB's 5V rail so we'll have to do some additional testing to see what the actual load on the USB bus will be.

  • 0 in reply to George Ioakimedes
    TI__Guru**** 151420 points

    If the 150 mA burst lasts for more than a couple of switching cycles (let's say more than 10 uS), then the IC will see that burst and attempt to react--it will increase the duty cycle and deliver more power to the load.  This will draw more input current.  If the burst is less than a few switching cycles, it will be supplied entirely by the output capacitors with only a slight increase in duty cycle to recharge them several cycles later.

  • 0 in reply to Chris Glaser
    Genius 4950 points

    Since you seem to be familiar with this product I thought I would ask you based on my application if you think a 4.7uH is going to be enough. I'm calculating ~500mA with a Vin=5V which seems way too high so I'm wondering if I'm going to need much larger inductance.

     

    Typically the thermal pad gets connected to ground but that doesn't seem to be the case for this product, is that correct? It looks like the EVM has it connected to ground but the datasheet doesn't say to do that unless I missed it.

  • 0 in reply to George Ioakimedes
    TI__Guru**** 151420 points

    Yes, the power pad should be connected to ground.  I agree it is hard tofind in this datasheet, but it is noted in note 1 on page 2.

    4.7 uH sounds right.  Most of the datasheet data was taken with that value inductor.  The list of inductors on page 25 would all be good choices.

    Yes, the peak inductor current will be above 500 mA, per equation 3.  Remember that this is a boost converter, so the current in the switch (and in the inductor) is always much greater than the load current.