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TPS54240 ENABLE AND UVLO (EN PIN)

Francesc Pages
Prodigy 40 points
Other Parts Discussed in Thread: TPS54240, TPS54340, TLV431B

Hello we are testing our prototypes. We develop a product that use A TPS54240 as DC/DC converter 24 to 12 Volts.

We have made the electronic circuit to start at 24.3 and stop at 19,5. We tested with realimentation from 12Volts and without.

Initiali it works fine but, when we test the same with several circuits 4 or more, we detect that start voltage is changing a lot between circuits and the problem is not in resistences, please can you anyone answer the next doubts in the documentation:

-- When we have 24Vin which is the Enable threshold voltage "in datasheet puts 1.25 typycal, but It seems that they are more near 1.2"

-- We see in datasheet that Enable threshold min is 1.15 and max is 1.36 (Is this correct? ) Is possible that two circuits at the same conditions, one have min and another max, or this min and max only refers a variation with temperature? It seems that with this variation we can not adjunt correctly the Start voltage? Is there any option to have this value more acurate?

-- are correct the specifications in datasheet of Input current and hysteresis current? We have done some test and we detect, that tps54240 seems more like tps54340 specifications.

Thanks a lot

  • 0
    TI__Mastermind 35115 points

    Hi Francesc,

    The specifications on the datasheet are correct. Most of the variation in the threshold will come from variation in the threshold voltage. The voltage can easily vary from 1.2V to 1.27V from unit to unit and this is the main source of the variation. There is almost no variation over temperature.

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 40 points

    Hi Anthony, thanks a lot for your answer.

    We are worried because we think that the  variation of threshold voltage is from the Vin. If you are right and the variation in unit to unit can be easily from 1.2 to 1.27, then we have to put another circuit before, because this treshold variation is 5,8% and therefore in our case in 24V the start voltage can vary  1,4V.

    We have done a little search, can you give a solution?  We found the next solution (we will do some variation, because the retroalimentation, we will catch from TPS output) based on TLV431B (0,5%).

    Is there some another solution to have a better accuracy in start threshold?

    Thanks a lot,

  • 0 in reply to Francesc Pages
    TI__Mastermind 35115 points

    The solution you post looks like it can work well. An alternative for good accuracy could be a supervisor/reset IC.