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TPS7A7300 Digital Pot

Ferdinand Cuevas
Prodigy 50 points
Other Parts Discussed in Thread: TPS7A7300

hi,

  I'd like to use a TPS7A7300 linear regulator with a digital pot. Can I use the FB pin to have a vout of 0.9v to 1.05v?   Can I adjust Vout up to 5v with a digital pot?

  I'll be disconnecting the sense pin and the configuration resistors if I use the digital pot, I assume this is the right way of doing it.

  Is there any other consideration of using a digital pot on TPS7A7300?

  Thanks

 

rdgs

Ferdie

  • 0
    TI__Guru 55940 points

    Hi Ferdie,

    Using the more traditional resistor divider method on the FB pin of the device, the output can be set to between 0.9V and 5V.  You are correct that you would want to leave the sense pin and ANYOUT pins floating as demonstrated in Figure 40 of the datasheet:

    Please note that due to any capacitance associated with the digital pot, it would be better to replace R1 with the pot.  The capacitance would act as a feedforward capacitor.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 50 points

    hi Ryan,

      Thanks for the reply.  Can I make R1 a pot while R2 a digital pot?  I need to remotely control the output voltage

    that why i need to put a digital pot in there?

    rdgs

    ferdie 

  • 0 in reply to Ferdinand Cuevas
    TI__Guru 55940 points

    Hi Ferdie,

    I apologize if I was not clear.  I am recommending to make R1 the digital pot and leave R2 as a fixed resistor.  Changing R1 or R2 will change the the output voltage based on the equation Vout = (R1 + R2) / R2 x 0.5.  We recommend that R2 be in the range of 27k to 33k in order to maintain the specified regulation accuracy.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 50 points

    hi Ryan,

      thanks for the reply. Do you have a recommended TI digital potentiometer that could work well with TPS7A7300?

    rdgs

    ferdie

  • 0 in reply to Ferdinand Cuevas
    TI__Guru 55940 points

    Hi Ferdie,

    I do not have a recommended digital pot; however, one thing that may be of interest to you is an App Note that describes how to use an I2C IO Expander Device to control Vout using the ANYOUT pins: 

    http://www.ti.com/lit/an/sbva035/sbva035.pdf?DCMP=analog_power_mr&HQS=tps7a7200-pran-in

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Prodigy 50 points

    hi Ryan,

      Thanks for the document but I need less than 50mV resolution so I need to stick to a digital potentiometer.

      You mentioned before that R2 needs to be in a range of 27K to 33K, is this the minimum value of R2? 

      Usually the digital potentiometer is in the range of 10K to 100K. If I fixed R2 to 27K, and I used a 10K pot, then effectively R2 will be bigger than 33K. Is this ok?

     

    rdgs

    ferdie 

  • 0 in reply to Ferdinand Cuevas
    Prodigy 50 points

    hi Ryan,

       I think I'm going to use a 50K pot for R1 and then a fix 47K on R2. Can this setting maintain the regulation accuracy of the regulator?

       Thanks

     

    rdgs

    ferdie

  • 0 in reply to Ferdinand Cuevas
    TI__Guru 55940 points

    Hi Ferdie,

    As mentioned above and in the datasheet, R2 needs to be in the range of 27k and 33k in order to maintain the specified regulation accuracy.  If you use a 47k resistor for R2, you are outside of the range.

    Very Respectfully,

    Ryan