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Original question:

TPS23754-1: Regarding TPS23754-1(TPS23754PWPR-1) 802.3at POE design question

TPS23754: Query on Heat dissipation

saranya narayanan
Prodigy 10 points
Part Number: TPS23754

Tool/software:

Hi  
 

We are using the PD Controller TPS23754 in our project. For thermal simulation, we require the heat dissipation of the IC. From the datasheet, we noted that the main supply voltages include Vc, VDD, and VB, and that the operating current for Vc @ 12 V is specified as 0.92 mA. So the heat dissipation can be estimate as 12 x 0.92=11.04mW

Could you please confirm whether any other supply rails we need to consider? Also what will be the operating current on VDD, VB?

  • +1
    TI__Intellectual 810 points

    Hi Saranya,

    Thank you for reaching out.


    I would suggest you consider the power dissipation from RTN, VC and VDD.


    RTN: With the maximum continues pass current 825 mA, the power dissipation (with highest hotswap MOSFET Rdson) could be 0.75 Ohm * 825 mA * 825 mA = 0.54 W.
    VC: With 12 V and 1.2 mA, the power dissipation would be 0.014 W.

    VDD: the continuous current would be less then 1mA and it would not have a major impact on total power dissipation.


    VB pin has a maximum sourcing current of 5mA, just for your reference. 



    Best regards,

    Zhining

  • 0 in reply to Zhining Zhang
    Prodigy 10 points

    Hi Zhining,

    Thank you for responding..!

    I have one more doubt. Should we have to consider the power dissipation of this 50 mE resistor?

  • 0 in reply to saranya narayanan
    TI__Intellectual 810 points

    Hi Saranya,

    You may include this resistor besides the MOSFET Rdson.

    It will conduct the RTN current as I have posted above.

    Best regards,

    Zhining

  • 0 in reply to Zhining Zhang
    Prodigy 10 points

    Hi Zhining Zhang

    If VDD = 48 V and the current is 1 mA, this results in a power dissipation of about 48 mW, which could affect our thermal simulation. Could you confirm whether this current flows only during startup or all over the operation of IC?

  • 0 in reply to saranya narayanan
    TI__Intellectual 810 points

    Hi Saranya,

    The VDD current we mentioned here is the current for continuous operation. Since you are talking about thermal simulation, I assume you are evaluating the thermal performance for continuous operation. 
    The VDD continuous current is expected to be smaller than 1mA. You might use 1mA in your thermal evaluation as reasonable assumption.

    Best regards,

    Zhining