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TPS61040 - for phantom power +48v and variable voltage

Other Parts Discussed in Thread: TPS61040, TPS61170

Hello, I am working on a USB powered audio device that needs phantom power (48v @ 4mA total).

1. Phantom Power

I'm using an the phantom example in the TPS61170 datasheet adapted for use with the a TPS61040.  It's working very nicely at 48v, but I would welcome any criticism, watch-outs, or suggestions for the following design:

Variable Voltage

In order to offer a low-power mode, I'd like to be able to switch to a lower voltage Phantom spec, and I was wondering if anybody's had any experience with this.  Would it be safe to switch in a resistor in parallel with R2 using a FET or a 4066-type switch?  

I would appreciate any advice on this matter.  Thank you!  

  • the circuit is good. but the input voltage of tps61040 should be 1.8~6V. make sure that Vout is lower than max voltage during transient, such as startup, load transient and Vout  switching using FB pin. thanks

    boost converter solution team

    jasper li

  • Thanks Jasper, you're right, I was adapting the schematic for a picture and forgot to fix the input voltage.  It will be getting 5v from USB.  

    Can you clarify "load transient and Vout  switching using FB pin," I'm not sure I understand what you mean here.  Is there an Application Note that I could read to get a greater understanding?  

  • Load transient : the load change from 0mA to 100mA for example. 

    Vout switching: because you mentioned that you want to change the Vout using a mosfet and a resistor in parallel with R2

    Jasper li

  • Ah!  I believe I understand now, that helps me to parse the sentence better.  

    So you think the mosfet switching could work reasonably as long as I do not let Vout exceed spec in the process?  That was what I was hoping.  

    According to the datasheet, the part is not spec'd for 48v, but if I keep Vout within wattage specifications and hold the part in SHUTDOWN when switching R2, would you say this is a reasonably safe approach for preserving the life of the TPS61040?  

  • the answer is yes for both of your question.  

    jasper Li

  • Thanks again Jasper, I'll post again here if anything comes up.  Your advice is much appreciated!