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CSD95480RWJ: How to specify current rating of power stage?

user4811888
Intellectual 530 points
Part Number: CSD95480RWJ
Other Parts Discussed in Thread: CSD17556Q5B, TPS543B20

Hi expert,

I‘ve found below spec of 70A continuous current and 90A peak current below, however no comments or explanations behind in datasheet.

Could l learn that how these two values are decided and what's the physical meaning  behind? SOA or based on thermal with evaluation board?

Please refer to below CSD17556Q5B datasheet, each current rating has its own detailed physical meaning, and they're specified according to SOA.

  • 0
    TI__Intellectual 795 points

    Hi,

    I'm looking into it and respond by tomorrow.

  • 0
    TI__Genius 10000 points

    Hi,

    70A continuous current is the DC current spec, accounting for thermal considerations. 90A peak spec is for transient events, where there is less thermal concerns, since the current is not present very long.

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Intellectual 530 points

    Hi,

    thanks for answering but it still looks so rough to me.

    What is the thermal condition, is it with EVB or with fans/heat-sink, and what is the allowable temperature rising?

    Why I ask this is because what I see from real application to share, is 20~30A per phase, much lower than 70A it claims.

    90A peak is also hard to understand, because such peak current cannot damage DrMOS and cannot cause thermal issue, is it defined with OCP point?  

  • 0 in reply to user4811888
    TI__Genius 10000 points

    Hi, 

    Murali is getting feedback from the team on this, but there are some on vacation. Please expect feedback early next week. Sorry for the delay!

    Thanks,

    Nastasha 

  • 0 in reply to Nastasha
    Intellectual 530 points

    Hi Nastasha and Muirail,

    thanks for both of you, I've also checked similar applicatinos of TI high current buck DC-DC, the output current is also claimed in real applications and tested on board in real system.

    Below is screenshot from TPS543B20, it claims 25A output current capbility, I can see very clearly why 25A is claimed for this part.

  • 0 in reply to user4811888
    TI__Intellectual 795 points

    Hi,

    70A current limitation comes from silicon limitation (Electromigration and current density) and 90A peak current is based on thermal limitation based on a current pulse of 50us duration as described in the NOTE3 which is shown below (i.e CSD95480's junction temperature reaches 125degC if 90A is applied for 50us duration)

    Thanks,

    Murali

  • 0 in reply to Murali Malla
    Intellectual 530 points

    Hi Murail,

    Typically, silicon limitation for generalized MOSFET is defined below:

    It is also thermally limited by Pmax and under condunction only. However, in the datasheet of CSD95xxx power stage, you can also see fsw=500kHz and switching conditions(VIN VOUT) also over there. 

    So could I conclude that in such kind of product, ID is not calcualted under condunction only, but is a complex functino of both switching and conduction loss in real application, correct？

  • 0 in reply to user4811888
    TI__Intellectual 795 points

    Your understanding and calculations are correct if the maximum current is limited by device junction temperature.

    In the case of CSD95480, the maximum continuous current limitation comes from electromigration and current density within the device.