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TPS92512 and TPS92513

Edward Stoneham
Prodigy 20 points

The data sheets for the TPS9251x series LED drivers provide an equation (#16 on page 14) for the AC losses due to MOSFET transitions. The loss values given by this equation are typically the largest of all of the losses in the driver. For instance, with a switching frequency of 1 MHz, an input voltage of 50 V, and an LED current of 1.5 A the equation gives a power loss of 2.7 W, which by itself is well more than enough to overheat the chip. Is this equation correct?

As a related question, is the MOSFET switch in these chips a PMOSFET or an NMOSFET?

-Ed

  • 0
    TI__Mastermind 25500 points
    That equation is an estimate based on measured slew rates for the switch at a certain operating condition, so it will not be exact (in this case it will likely not be quite that high since the SR tends to be slightly faster and higher input voltages), but it will likely not be way too far off. That being said, there is a reason people generally do not use high switching frequencies at high voltages and this is one of them along with the higher switching Iq required for switching faster which also heats up the chip. You can always put a thermal camera on it to be sure, but at 50V input you will most likely want to reduce the switching frequency significantly.
    As for the internal FET, it is N channel which reduces Rds(on)/area but also is why bootstrapping is required.
  • 0 in reply to Clinton Jensen
    Prodigy 20 points

    Thank you Clinton, Your answer is very helpful and informative.