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TPS2376-H: UVLO

Erin Zhang
Prodigy 130 points
Part Number: TPS2376-H

Hello,

Very urgent ! The customer  wants to know whether the resistance of the UVLO in the picture is right or not and how to choose the proper resistance.

Thanks and best regards,

Erin

  • 0
    TI__Genius 9230 points

    Hello Erin,

    To answer the customer's question, yes, this is the correct resistance to allow for the UVLO resistor divider to also be used for detection; however, I would NOT recommend this configuration. 

    It is better to place the 24.9k ohm resistor from VDD to DEN and use much larger resistor values (as large as possible) than what is shown in that figure for the UVLO pin. Be sure to pick a divider ratio that provides the correct voltage at the UVLO pin according to the table on page 4 of SLVS646A while satisfying the customer’s intended turn-on (max 42V) & turn-off voltages (min 30V).

    Thanks,
    Thomas A.

  • 0 in reply to Thomas Amlee
    TI__Genius 9230 points
    Also, be sure to carefully size the bottom resistance of the divider to account for any leakage current into the UVLO pin itself.
  • 0 in reply to Thomas Amlee
    Prodigy 130 points
    Hello Thomas,

    The customer use resistance in the figure above and the PD controller didn't work. And we place the larger resistor as you said , the PD functioned well. The customer wants to know why should we use larger resistor.
    Thanks for your kindly help.

    best regards,
    Erin
  • 0 in reply to Erin Zhang
    TI__Genius 9230 points
    Hello Erin,

    The main thing is that they are guaranteed to pass detection by putting attaching the 24.9k ohm resistor to DEN & VDD.

    Once the 24.9k ohm resistor is sensed by the PSE during detection, the DEN pin is no longer needed, so a FET in the DEN pin closes, preventing current leakage into the DEN pin during operation.

    If they used the configuration in figure 1 of SLVS646A (www.ti.com/.../tps2376-h.pdf), they would always be drawing the same amount of detection current away from the load (~2mA). The UVLO pin does not need this amount of current to work properly. It just needs the proper voltage provided by the ratio between the resistors.

    As long as the voltage divider ratio is maintained, both resistances can be proportionally scaled to reduce the leakage current going though the UVLO pin, allowing more power to transfer to the load, improving efficiency.

    The amount that these resistance can be scaled should be as high as realistically possible.

    Thanks,
    Thomas A.
  • 0 in reply to Thomas Amlee
    Prodigy 130 points
    Hello Thomas，

    Thanks a lot for your kindly help

    best regards，
    Erin