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PTN78000AAH Maximum Output Current and Temperature Derating

Dominique Megran
Prodigy 30 points
Other Parts Discussed in Thread: PTN78060A

Our product uses a PTN78000AAH voltage regulator module with a 24V input and a -15V output.  I have discovered that the regulator is supplying approximately 0.75A continuously.  The datasheet maximum output current is 0.6A at -15V with an ambient temperature of 85°C with natural convection airflow.

Our product's upper ambient temperature specification for the equipment is 49°C.  Let's assume that the ambient temperature of the regulator is somewhat higher at 55°C in the case with natural convection airflow.  If I extrapolate the temperature derating vs. output current curve for a 12V input (the 24V input curve isn't given in the datasheet for a -15V output) it is approximately 0.75A at 55°C.  I know that this doesn't give much margin, but can I interpret the curve this way, or will this lead to potential early failures?  If so, is there the curve available for a 24V input a -15V output?

I could upgrade to the PTN78060A, but it is not footprint compatible and would require a board spin.  For you information we are using 2 oz. copper.

I appreciate any feedback.

Thanks,

Dom Megran

  • 0
    TI__Mastermind 38230 points

    PTN78000AAH maximum input voltage with (-)15Vout is +17V. ThePTN78XXXAXX  Modules absolute maximum Vin is =17V with Vout (-) 15V. Buck boost absolute voltage  Vin+Vout=32V. The PTN must not be used with 24Vin. The PTN78000AAH maximum output current (-15VOut) is limited to 600mA with either (+) 12Vin or (+)15Vin.

    There are several alternative power solutions fo (-)15Vout at 750mA.  

    Convert +24V to either +12V or +15V with a   step down regulator.

    1. PTH78000HAx can be used to down convert  from + 24V in to +15Vout .Maximum ambient temperatures  with no  air flow  WITH 1A output current is 80°C

    1. Add a front  power device with input of (+)24V and output of (+)15V. Then connect (+)15V to the  PTN78060AAx input  voltage pin. The output voltage can be adjusted to (-) 15V at 750mA.

    a. The PTN78060AAx thermal section(SOA) of the data  sheet  with no air flow at (-)15V Vout with 12V or 15Vin has a +70°C maximum ambient temperature with no air flow.

    Tom