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LM25069QUICK-CALC: Maximum FET Power Limit

Part Number: LM25069QUICK-CALC
Other Parts Discussed in Thread: CSD17553Q5A, TPS25982, LM25069

Hi team,

Could you please comment on how to determine the desired max. FET power limit if engineers choose CSD17553Q5A? 3.1W?

Considering the current accuracy, is there a lowest limit?

Best regards,

Sam Ting

 

  • Hi Sam Ting,

    You can use the SOA chart in step-8 of the design calculator to select a appropriate Power limit value. 

    The Green line (SOA) should be always greater than the blue line (MAX) line in the graph

    Can you let me know the following system level specifications so that I can suggest you a suitable value

    • Vin(Max):
    • Max Load Current:
    • Desired Current limit Value:
    • Total Output Capacitance:
    • FET Selected:
    • No. of FET's:
    • Max Ambient Temp in your system:
    • Estimated RQJA of the FET's in your system:

  • Hi Praveen,

    Please find the specs below, thanks for your support!

    • Vin(Max): 13.2V 
    • Max Load Current: 13A
    • Desired Current limit Value: >=15A
    • Total Output Capacitance: 1200uF
    • FET Selected: CSD17553Q5A
    • No. of FET's: 1
    • Max Ambient Temp in your system: 60°C
    • Estimated RQJA of the FET's in your system: 40.5°C/W (according to CSD17553Q5A datasheet)

    Best regards,

    Sam Ting

  • Hi Sam Ting,

    TPS25982 efuse seems to a exact fit for you application. You will save on cost and size (FET being integrated) and have more features like programmable no. of retries and retry delay, adjustable over current blanking duration and LDSTRT feature.

    Do let me us know if this device is suitable for your application.

    For your design with LM25069, you can consider,

    • Rsns = 3 mohms
    • Rpwr  = 23.7 kohms
    • Timer Capacitor  = 220 nF