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Original question:

UCC28180: UCC28180D

UCC28180: UCC28180: Isense noise related failure

Pravin Iyengar
Prodigy 190 points
Part Number: UCC28180

Good morning,

I've developed a 3.5kW PFC using the UCC28180 controller IC for an audio amplifier. Due to the dynamic loading nature of the amp, the SOC and PCL of the IC are overridden by using a low value of sense resistor. In this case I am using 4x 8mR sense resistors, to set the SOC at 129, as the PFC peak currents can reach to 90A for a couple of cycles during dynamic loading. During normal operation the loading is less than 30Arms.

 I am now having a problem which I think is noise related in the Isense line. Under normal loading as I increase the load gradually to just beyond 15Arms, I can see a fuzz start to appear at the top of the sine wave current. If I keep increase the PFC fails, short circuiting the FETs. I used to think it had something to do with the miller oscillations in the FETS, but that has now been suppressed by slowing them down and the problem still persists.

I suspect the noise in the track coming from the sense resistor to the IC is causing some instability to the controller. Please could someone have a look at it and suggest a possible fix.

The long blue tracks below are the current sense line feeding back to controller IC U15. I was initially using BAT54 negative clamp diode. Having read on data sheet that the voltage drop needs to be between -0.4 and -1.1V, I realised the schottky voltage drop is much lower. So i replaced it with LS4148. It offered some improvement I think as I was able to load the power supply some more before I started seeing the fuzz.

I look forward to some feedback. Thank you.

Regards

Pravin

  • 0
    TI__Mastermind 34465 points

    Hello Pravin,

    I believe your assumption about noise pickup is correct.
    Your current sense lines are certainly routed  a long way from the controller ic and also it seems there is a long narrow path between
    the signal ground (pin 1) and the power ground (source of boost FETs)

    It looks like there is enough room on the pcb to move the UCC28180 and all the controller components up beside the current sense resistors.
    Your other option is to cut the ground trace vias and add a wire to directly connects grounds. You should test this anyway and see how much it improves performance. Also cut the sense leads on the 8mR resistor and add a twisted wire pair in order to test the circuit.
    Or perhaps you can just move the current sense resistors away from the bridge rectifier and closer to the controller ?

    Do you have a 220R 1nF filter on the ISENSE pin ?

    How accurate an overcurrent value you can get is related to how good a layout can be achieved. So if your overcurrent value can be increased you should investigate decreasing the current sense resistor value. 

    Regards

    John