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worst case Pc(max Vcc/Icc/Vo/Io)

Other Parts Discussed in Thread: PCA9555, PCA9545A

I find datasheet ,but lack some  information.

Pc need provide the worst case Pc(max Vcc/Icc/Vo/Io)

I used to find the TI engineer, He recommends update my question into TI E2E.

Part Description

Θja (C/W)

Θjc (C/W)

Maximum Tj

Power consumption

Supplier

S IC SN74LVC1G17DCKR SC70 5P BUFFER

280

66

125

TI

S IC PCA9555RGER VQFN24P I2C IO EXPANDER

45

 

150

 

TI

S IC SN74LVC1G04DCKR SC-70 5P INVER

278

93 

150

 

TI

S IC PCA9545APWR TSSOP 20P SWITCH

83

 

150

0.4

TI

  • Hi,

    I can comment on the two logic devices listed above.

    The SN74LVC1G17DCKR Maximum Tj is 150C, not 125C (that's the maximum TA).

    Power consumption for both SN74LVC1G17DCKR and SN74LVC1G04DCKR is dependent on switching frequency and loading conditions. I would recommend using the method set forth in this application report: CMOS Power Consumption and Cpd Calculation

  • Hello,

    I've placed thermal modeling requests in for the PCA9555 and PCA9545A devices you've requested, it should take a few days before I hear back the results for theta-jc.

    power consumption depends on multiple conditions such as Vcc and the data you are sending and what frequency (for the I2C switch and IO expander SDA/SCL pins). The GPIO expander will also depend on if you are using it as an input or output, and the set up (schematics).

    -Bobby
  • Hello,

    Thermal data for PCA9545APWR in terms of Theta JA is 97.7C/W. I haven't received data back yet on the other request just. I've looped in another member of my team who will get back to you on this when there has been a update (I will be Out of the Office for the next two weeks).

    Thanks,
    -Bobby
  • Sorry to bother you, If I will calculate the Ptot this photo show parameter is it enough?

    If I lack parameter, the parameter commonly used what?

  • Hello,

    I am not sure what your question is, but I will try and answer what I think you are trying to say.

    If you have the power dissipation that is seen by the device then you can calculate the junction temperature (TJ) assuming you know the ambient air temp (TA) and have the thermal resistance from air to junction (JA).

    There are a few things that must be high lighted because this method is simplified and make a lot of assumptions.

    The thermal resistance from air to the junction of the device is done using a JEDEC standard for this package. It assumes no other components on the board that could add power dissipation and affect the junction temperature of the device under test. It also assumes the board orientation and natural convection with a standardized air environment.

    Unless you have advanced thermal modeling software then it is often best to take measurements of the case temperature (TC) and use the thermal resistance from Case to Junction (JC), which is not dependent on the JEDEC standards and is much less dependent on outside factors. You will have to measure the input power and the output power then calculated the difference between them, that will be the power dissipated in the part (PDISS). You will have to then measure TC. This will allow you to calculate TJ.


    Usually you have to measure the power dissipation but if not you can use the max quiescent current at the operating voltage to determine min power dissipation. 

    Here is a link to additional reference material. 

    http://www.ti.com/lit/an/spra953c/spra953c.pdf

    Let me know if I have not answered your questions.

    -Francis

  • Hi
    I am very grateful for your help.
    Sorry, what I meant is the IC in worst case (I don't know design used Vcc,Hz…)
    1)Total Power
    2)TC. or (JC)
  • Hello,

    If you need an absolutely max power dissipation of the part you could extrapolate it from the Tjmax (150C, but keep in mind this increases FIT numbers), Tamax,(85C and theta ja (45C/W).

    Keep in mind this assume JEDEC standard for this package.  Also, if the part is exposed to more than 100C at the junction the reliability of the device gets affected, which affect the FIT rate.  You may want to use 100C for Tj, which would give you a max Pdiss of 333mW without loss of reliability.

    We don't specify the max case temp.  The case withstand temperatures past what the max junction temperature is, so you can use that as a max if you want to be conservative.

    -Francis Houde

     

  • Thanks you help.

    The IC worst work doesn't  exceed 70C.

    I will apply 1.44W 

  • Hello,

    I want to explicitly state that this is not what the part dissipates, but rather is what the package can handle and what will keep the part from exceeding operational specifications.  Our part will not dissipate this much power unless this is something catastrophically wrong.  We will be dissipated on the order of mWatts not Watts.

    -Francis Houde