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PTB78560X input fuse blows

James Perry
Prodigy 30 points

I am experiencing an issue with a PTB78560CAH blowing a Litttlefuse PICO II P/N: 0472001.MAT1L one amp fuse used as input protection to the DC/DC converter.  The output load is under five milliamperes and consists of a 12 VDc brushless fan and electronic circuits. The PTB78560CAH is powered from an aircraft electrical system that uses generators and a lead acid gel battery as a power source with the source voltage between 26.5 VDC and 29.5 VDC; electrical loads in the aircraft that are operating when the PTB78560CAH is powered include several brush type electrical motors and a 400 Hz static inverter.  The input has two 0.1 uF capacitors in parrallel and two Nichicon 100 uf 63 VDC PW series capacitors in parallel to the input. 


Would increasing the fuse4 value to three amperes solve the problem, or is there another issue(s) that I should be thinking about.

  • 0
    TI__Mastermind 38230 points

    James;

    PTB78560CAH  has output over-current (OCP) protection. This OCP threshold  is about  3.75 Amps .If this threshold  is exceeded, the converter will fold back and  then shutdown . Once the output fault is removed ,the converter will function normally.

    If the  output current is below the  threshold (OCP)  or about  3.2 Amps,  prior to converter shutdown, average  input current will be about 2.84amps  worst case with  18Vin.

    A 3 amp fuse should  protect the power source,  input bus, from excessive high current  and which will  likely eliminate  random fuse failures.

    Tom

    If you have any additional questions, my direct e-mail address is tguerin@ti.com

  • 0 in reply to Tom Guerin
    Prodigy 30 points

    Thank you for the explanation and clarification of operation.

    James