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TPS2350 ATCA Reference Design Questions

Tom Schultz
Expert 4140 points
Other Parts Discussed in Thread: TPS2350

Hello,

I have a customer with a few questions on the TPS2350 ATCA Reference Design whitepaper (http://focus.ti.com/docs/toolsw/folders/print/tps2350atca.html).

Can you help to answer these?

1. What are the equations governing the size of C5 holdup cap in table 1, p.3? My calculations don’t match these values and I think that they would also be very dependent on the downstream regulator used (e.g. what it’s minimum input voltage is for regulation).

2.      2.  Why is R17 required and why would its value selected be dependent on the board’s overall power envelope?

3.       3. The board’s power consumption is very software dependent. So even if a board consumed 400W (ATCA max spec) during peak activity, other software applications might run the board at a much lower level like 100W when the software/OS is idling. How can a static R17 value be selected when the board’s power consumption is variable?

4.       4. What are the equations governing the size of R17 in table 1, p.3?

              Thanks,

                 Tom

 

  • 0
    TI__Expert 5640 points

    The hold up cap is calculated to provide a given voltage drop over time or constant dv/dt.  You can calculate the nominal current draw of the load in the table and divide it by the capacitance in the table.  This will be the same value for every row in the table.

    R17 sets the current limit and peak current limit for the TPS2350 to protect either the input power supply or the load.  It must be sized to accomodate the maximum current capabilities of the input or load.  Operating below this maximum current is okay (and advised).  So if R17 is sized for a 400W board, Then the TPS2350 can still power a 100W board okay. 

    Please see the TPS2350 datasheet for the equation to select R17 and a detailed description of the current limiting function.