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TPS54020: Enable and UVLO Adjustment

Expert 6030 points
Part Number: TPS54020
Other Parts Discussed in Thread: TPS54622, TPS54623, TPS54620

Team,

Section 8.3.8 of the TPS54020 datasheet lists the equations to calculate the start/stop input voltage.  However, the calculations do not result in the resistor values shown in the example on page 24 using 7.5 V and 7.1 V for the start and stop voltages.  

Looking at the EVM user's guide section 1.3.3, Ih and and Venrising are listed as different values.  Doing a TINA simulation, it appears the datasheet recommendations are more accurate than the EVM user guide recommendations.

Datasheet:

EVM:

What is the recommended Ih value for doing the UVLO resistor calculations?

Thanks,

Phil  

  • Hi Phil,

    Surprisingly this issue was pointed out to me by someone else earlier this week and I am in the process of correcting the datasheet. The 3.3 uA spec is not the hysteresis current, it is the total current when EN is above the threshold as described by the test conditions.The hysteresis current is difference of 3.3 uA and 1.15 uA. The EVM is correct in giving 2.15 uA for the hysteresis current. I will be changing the value listed for the equation and the description of the specification in the datasheet so that it is more clear.

    For the voltage thresholds, the datasheet number is more correct. However this won't make much of a difference because these are typical values only and they are about the same. What really matters are the min/max.

    I also noticed this mix up in the hysteresis current is in the TPS54620, TPS54622 and TPS54623 datasheets. There may be other parts in this family with the same mistake.

    Best Regards,
    Anthony

  • Thanks Anthony! We may want to loop in the Webench/Tina team also to double check how this device is modeled. When I was doing simulations, the startup occurred much closer to 7.5 V and the shutdown much closer to 7.1 V when the calculated values from the datasheet values were used. The EVM values resulted in higher thresholds.

    Phil
  • I forgot to mention I also checked an unencrypted model for this part I had on hand and it has the incorrect implementation of the hysteresis current. In other words the hysteresis current it uses is 3.3 uA when it should be 2.15 uA.