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TPSM82810: Device Query

Shinu.V.Mathew
Genius 10620 points
Part Number: TPSM82810
Other Parts Discussed in Thread: TPSM82816

Tool/software:

Hi Team,

Customer is having below query on webench simulation and default values selected, can you please help on the same. 

  1. For setting up the mode, why did Webench select 10k? I assume 1.8MHz FCCM mode is referring to table 8-1 in the datasheet (attach in the end of this mail). But as mentioned in our application we have approximately 104µF decoupling on the 1.1V supply, so wouldn’t 33k be a better selection?
  2. For selecting the frequency, what is the formula I should use to ensure I respect the minimum on time?
    1. From the datasheet we calculate D=Vout/Vin -> D=3.3/1.1 -> D=0.33.

fsmax=1/(tonmin * D -> fsmax = 1/(75ns * 0.3) -> fsmax=

This frequency seems too high

    1. When I apply these formulas in the example design on page 10, I cannot get the 2.67MHz. Is there something wrong with the formula?
  2. Why do you choose to connect MODE/SYNC to high, this forces PWM regardless of the load condition right?

Regards, S Mathew.

  • 0
    TI__Guru**** 150930 points

    Hi S Mathew,

    Yes, the default design is for a 1.8 MHz frequency with the least amount of Cout.  You can change this if you want to, but I would not recommend it.  The capacitances written are the actual, effective capacitances, which are lower than your nominal capacitance.  Your 104uF nominal may not give 60 uF effective.

    With a 3.3Vin, you should have no limits for minimum on time.  The maximum frequency should be very high.

    It looks like there is a typo in equation 2.  You can use the example from the TPSM82816 D/S.  It has a different value for the minimum on time, but the formula is fixed:

    Yes, MODE/SYNC is connected to VIN by default.  You can change this with the ModeSetting dropdown on the left.

    Chris