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TPS7A16-Q1: transient power rating

Part Number: TPS7A16-Q1

Team, 

My customer has the following question: 

I’m wondering if you have something like a Safe-Operating-Area (SOA) curve for the device mentioned in the subject line?  I usually see these curves for things like MOSFETs, but figured it wouldn’t hurt to ask for this device.

Our situation is that we typically have a 28V input and 5V output.  During the 50V 12.5ms transient to 50V, the device will be dissipating more power and I’m wondering if there’s any guidance for transient power rating?

Regards,

Aaron

  • Hi Aaron,

    Please allow some time for me to check if we have a SOA curve available for this device. If we don't have one, it normally takes 2 business days for us to generate one. In the mean time, you can also estimate the Safe-Operating-Area (SOA) using the thermal metrics provided in the datasheet.

    Here is another post that discussed in details how to estimate SOA, please see this link:

    Regards,
    Jason Song

  • Hi Aaron,

    We don't have a SOA curve for this device. For the application, what's the load current on the device when you have the 28V to 50V transitions?

    Regards,
    Jason

  • I am working with Aaron on this application...

    In the vast majority of conditions, the load current will be minimal... tens of microamps.

    There is one condition where it is possible (very unlikely) that the load current could be 30mA with a peak input voltage of 50V.  This time at 50V would be minimal, less than 15msec.

    That gives me a peak power dissipation of 1.35W for less than 15msec.  After 15msec, the power drops to 0.72W.

    If I use the datasheet value for ThetaJA, I could exceed the 150C junction temp limit.

    Thoughts?

  • Hi Benjamin,

    The thermal numbers like ThetaJA is for the estimation of temperature rise when the temperature has reached a steady state. Depending on what kind of boards you have, it could take 10s or longer for the junction temperature to be stabilized.

    Having 1.35W for only 15ms should give you probably less than 50% of the ThetaJA. What's the ambient temperature for the application? Which package do you have?

    Regards,
    Jason Song

  • Worst case ambient temp is 90C.  I am using the "HVSSOP" package (MSOP-8 with power pad)

    Our board will be relatively standard FR4, 1oz (or maybe 1.5oz) copper on the outer layers.

  • Hi Benjamin,

    For the HVSSOP, the Rthetaja = 66C/W, with 0.72W, the temp rise is around 47.52C. With the 90C ambient, the junction temperature is at 137.52. The recommended junction temperature is up to 125C. The 15ms high power at 1.35W will make it slightly worse, but due to the short period of the highpower, the estimated temperature rise could be much less than the one calculated using Rthetaja.

    My main concern here is that the thermal numbers listed on datasheet are the numbers using JEDEC standard, at customer's side, due to the size of their copper for cooling, their performance could vary. Continous running the device beyond 125C, the parts will have higher failure rate and the life span expectation will also be reduced.

    I would not recommend this device based on the 90C ambient and the expected power dissipation. Are they open to use other devices with different packages?

    Regards,
    Jason Song

  • A few clarifications...

    The 90C ambient is an intermittent condition.  The continuous ambient is ~75C, which gives me a junction temp of 122.5C.

    Also, the 0.72W is a condition lasting no more than a few minutes while a capacitor is being charged.  Once the cap is charged, the output current (and power) goes to almost zero.

  • Hi Benjamin,

    Thanks for the clarifications. If ambient is 75C, and the 0.72 W only last a few minutes with a peak power of 1.32W for 15ms, I don't think it will cause a thermal problem. As long as they are not running the device continously above 125C, it should be okay. But please advise the customer that the DPPM, MTBF, FIT rate published under the qulity page of the device is rated for a ambient at 55C, having it running continously at 75C will affect the numbers. 

    Regards,
    Jason Song