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TPS92682-Q1: Design procedure for Buck-Boost power supply

Richard Skeels1
Prodigy 40 points
Part Number: TPS92682-Q1
Other Parts Discussed in Thread: TPS92692-Q1

I'm looking at a design using the TPS92682-Q1 so for all my designs I generate a spreadsheet.to calculate the values.

As part of this I usually put a know design into my calculations to ensure that my spreadsheet results are working.

I've gone through 8.4.4 of the TPS92682-Q1 Datasheet that describes a Buck-Boost Design Procedure to use this to check my spreadsheet.

When I've got to 8.4.4.4 Inductor selection the value given for L is 23.4 uH 

I'm trying to get my spreadsheet to match this but even changing the values to VO , VIN & PO(BDRY) I can't get the values to match.

Is there stored anywhere the original values used for the equations in other examples I've seen on TI datasheets these values are given.

or does anyone have a spreadsheet that will calculate the values for a TPS92682-Q1 ?

  • 0
    Prodigy 40 points

    i've just spent some time going through the calculations again and found that PO(BDRY)  is mentioned in the design parameters in table 45.(3.5 W)

    this gives me the correct answer to my equation but I'm still trying to work out how PO(BDRY) is derived as from the datasheet PO(BDRY)  is derived from equation 15 on the TPS92682-Q1 datasheet.

    The equation is PO(BDRY) ≥ ILED(MIN) x VO(MIN)

    So using the parameters given in table 45 this would be ILED(MIN = 0.2 A and VO(MIN) = 8.4 V 

    Therefore PO(BDRY) ≥.1.68 W

    Can anyone answer this please ?

  • 0 in reply to Richard Skeels1
    TI__Mastermind 18890 points

    Hi Richard,

    For example 8.4.4 design procedure, we use Table 45 for the values and calculate the power stage components values.  For this we set Po(BDRY) as 3.5W (in the table) which is between 1/2 to 1/4 of the Po(max) of 12W.  This is using equation (16) on page 53 and just setting Po(BDRY) to be 3.5W.  Another word, you set this boundary condition to calculate your power stage values.

    You can also use equation 15 to give you different Po(BDRY) and therefore different inductor value.  It will work either way with different values the different is where it goes from continuous conduction mode to discontinuous mode.  It is your choice to choose whatever is appropriate for your design. 

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Prodigy 40 points

    Hello Tuan,

    Thank you for your help on this.

    I've just got to calculating the IQ(RMS) as per Equation 11, the equation when I use it comes out at approximately 700mA.

    I've investigated the equation and I believe that the term in the square root should be 1+VIN(MIN)/VO(MIN) not 1-VIN(MIN)/VO(MIN)

    I've checked against datasheet TPS92692-Q1 and the same equation (TPS92692-Q1 is equation 24) uses 1+VIN(MIN)/VO(MIN) 

    Can you confirm this please.

    Regards Richard

  • 0 in reply to Richard Skeels1
    TI__Mastermind 18890 points

    Hi Richard,

    You are correct.  For Buck Boost, the 1+VIN(MIN)/VO(MIN) and not minus.  The data sheet will be corrected on the next update.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Prodigy 40 points

    Hello Tuan,

    has anyone generated a spreadsheet to work out the correct values for this part ?

    I notice that there isn't a Web Bench for it yet ?

    Kind Regards 

    Richard

  • 0 in reply to Richard Skeels1
    TI__Mastermind 18890 points

    Hi Richard,

    There is not a spread sheet or Web Bench generated for this part yet.  We are working on it and will post it as soon as we are done.

    Just a note...Please post a new thread if you have a new question instead of posting onto an old thread that has been answered.  That will help user to search answer more easily and for us to keep track.

    Thanks Tuan