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TPS2491: Short Circuit Recovery

Part Number: TPS2491
Other Parts Discussed in Thread: TPS2419

Not sure if it is a design or assembly issue!

The device will properly shutdown when a short is connected across the output, but multiple boards are not recovering from shutdown. The device will recover however if the output power is cycled.

Design criteria for TPS2419:

  • Vcc=EN=28VDC,
  • PROG=VREF=4V,
  • Rsense=0.062 Ohm,
  • Ct=1nF,
  • Cout =11uF,
  • Cbypass=0.1uF,
  • Cin=10uF.
  • Load=140Ohm resistor (0.2A),
  • Q=STL70N10F with 10 Ohm in series gate resistor. 
  • Circuit tested @ +25C.

 

The controller implemented at the output of a 28VDC  DC-DC SEPIC converter, current limit to 0.3A.

The first 50+ circuits worked flawlessly, The latest batch of 10 units has 60% failure rate.

Increased Ct to 10nF+1nF=11nF in all failed units, at least two units still do not recover after short to ground were removed.

 

Question:

1)  Does Ct has a minimum capacitance value?

2)  Is there a minimum restart time or fault timer for this controller?

Thank you,

Ryan

  • Hi Ryan,

    To answer both of your questions, Ct does not have a min. cap value, but we usually recommend a Ct value of 2.2nF or higher (0.35ms fault time). This is because if the fault timer is set within a couple of microseconds,  any type of transient can cause the FET to shutoff and cause unwanted nuisance trips.  

    Let's try and solve this problem. The easiest way to do this is to please provide (or have your customer fill out) our design calculator tool with this device and attach. This will help review and troubleshoot your design, and would greatly speed up the back-forth communication of questions we would have for information needed for the review (such as Rpower value, nominal load current, Vin range, total output cap including anything connected downstream from the output node, which may not be shown on a partial schematic, etc.)

    You can find it by going to www.ti.com/hotswap ==> click on “Tools & software” ==> then click on “Hot Swap design calculator tools”

    For help on filling out the cells on the excel spreadsheet, our team created video tutorials on how to fill out the hot-swap design calculator spreadsheet. They explain cell by cell what each one means and how to enter the correct value. The videos are at www.ti.com/hotswap ==> Click on “Support & Training” tab.

    Also, if you can provide a picture of the schematic showing our part with all of the necessary component connections and values, that would be great :-) 

    Best Regards,

    Aramis P. Alvarez