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TPS40090: Setting the switching frequency

Ammar Afi
Prodigy 110 points
Part Number: TPS40090

Hello,

1. I'm trying to understand the formula for setting up the switching frequency of TPS40090. How did the formula has the 39.2x10^3 and why fph need to power up by -1.024?

2. Is TPS40090 able to work on single phase?. The datasheet has mentioned that it is able to program with two, three and four phases.

Thanks.

  • 0
    TI__Mastermind 24075 points

    Hi Ammar, 

    1. Sorry, I can not find the answer.  I guess the equation is extracted from the figure 3 curve on datasheet, and the figure 3 curve is from the actual test result. 

    2. TPS40090 was designed for 2/3/4 phase operation. It may work at single phase, but we did not test it at single phase and we don't know if there is any problem. For single phase application, I suggest to consider other part. 

    Thanks

    Qian

  • 0 in reply to Qian Chen
    Prodigy 110 points

    Hi Qian,

    1. Do you know why fph need to power up by -1.024? 

    In the TPS40090EVM-002 design guide, the frequency set up for each phase is 420kHz and Rt is calculated to be 65.8kOhm,

    Do you able to get it by plucking this value in the given formula?

    2. So is the best way to get the value of Rt by looking at the graph in figure 3?

    Thanks.

  • 0 in reply to Ammar Afi
    TI__Mastermind 24075 points

    Hi Ammar, 

    1. Based on calculation, with phase frequency at 420kHz, the Rt should be 73.7kHz. Looks like the equation is not very accurate at this frequency region. 

    As I said, I guess the equation is extracted from the figure 3 curve, and that's how -1.024 comes from.

    Also, as the curve is not linear, one equation is not able to match the curve well in whole frequency region. That's means the equation is not very accurate at some frequency region. 

    2. I think you can use figure 3 curve to find the Rt value. The curve if for 4 phase.

    For 2phase and 3phase, multiple Rt value by kph (1.33).

    Thanks

    Qian