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TPS2553 Fault issue

Frederic Jutras
Prodigy 100 points
Other Parts Discussed in Thread: TPS2553

Hello everyone, 

We are using a TPS2553 in our design to monitor an auxiliary supply and make sure that it's not passing over a certain limit. (in our case 155mA) We are not using the -1 (latch off version) which is perfect cause we still want to have a current even if the load is too high. The unit does limit the current at the proper value on the eval board (by changing values of some caps/resistor) as well as the designed board we created base on the eval board results. 

Where we have an issue is in regard of the fault pin. The fault get drain on the eval board but not on the unit we created. I was wondering if there is some information I should have read to help figure out why only the fault pin isn't working.  

In our desing we have a 100nF input cap only (supply with 3V3), 10uF caps output and a 100k pull up on the fault pin. the input/output voltage are connected to the unit thru traces and not plane like the eval board. 

Let me know if you have any suggestion

Thanks

Frederic Jutras

  • 0
    TI__Mastermind 42795 points

    I agree that the problem seems PCB layout related. Try lab experiments such as relocating the IN capacitor and ILIM resistor so that they are very close to the TPS2553. Capture all voltage waveforms when the fault occurs as this can help with circuit debug.

  • 0 in reply to Eric Wright
    Prodigy 100 points

    Eric, 

    I tried relocated the input caps as you suggested (as well as adding a second cap 10uF) and still no fault signal. I place the caps right on pins 1 and 2 of the IC. I also added a 220µF over the output since we only have a 10µF and the eval board have a 150uF. That did not help neither.. (none of the mods were removed) then I moved the ILIM resistor right over the IC (package was long enough) between pin 5 and 2. Nothing of that helps. I was doubting the part so I removed it from the board and place it on the eval board.. It was working just fine.. 

    Have any suggestion?

    Thanks

    Fred