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UCC27524: Short circuit - after changing to UCC27524ASOIC8 DUAL

Shahaf Gargir
Prodigy 315 points
Part Number: UCC27524
Other Parts Discussed in Thread: UCC27424

Hi team,

the coustomer gets short circuit after changing from UCC27424D SOIC8 DUAL to UCC27524ASOIC8 DUAL device, the circuit worked ok before the assembeling of the new part with the older part.

have you encounterd a similar problem?

what can cause this problem?

thanks,

shahaf

  • 0
    TI__Mastermind 22995 points
    Hello Shahaf,
    We regret the customer has a concern with the UCC27524 in their application. To be able to answer the question can you give some more details.
    The short circuit you refer, is this a short on the driver output, or power device(s) being driven from the driver?
    Is it possible to get at least a partial schematic, so I can review and make suggestions.

    Richard
  • 0 in reply to Richard Herring
    Prodigy 20 points

    Hi Richard 

    the short circuit is on one of the outputs (both output's  connected directly to the gate of the FET ) 

    The circuit is a buck converter, and this driver is for the low side FET.

    both inputs connected together to a 5v logic. 

    both enable connected together to a 5v logic. 

    supply is 12v, switching frequency is 200khz. 

    Timing: as we turn off the high side FET the inputs to the low side driver go high when zero voltage is detected on the low side FET enable inputs to go high. 

    There is no issue of cross conduction, but some time due to noise problem the inputs go low for a very short time (about 20 nSEC) so that as soon as the body diode of the  low 

    side FET start to conduct, the driver go high for a very short time, go low, and then go high again.

    as there is no limitation in the spec on the driver on minimum pw , do you think this is the problem?

  • 0 in reply to Richard Herring
    TI__Prodigy 315 points

     Hi Richard,

    i adding the schematic.  

    thanks,

    shahaf

    buck.pdf

  • 0 in reply to moshe kalechstain
    TI__Mastermind 22995 points

    Hello Shahaf,

    I think the issue is with the connecting of the UCC27524 outputs directly together, without any gate resistance from each driver output and the separate gate resistors connected to the gate of the FET. Difference in prop delay of the two driver channels can result in cross conduction between the driver channels.

    The UCC27424 is better suited for connecting directly in parallel due to the bipolar/FET output structure, and the switching times are a little slower.

    For connecting driver channels directly in parallel we recommend the UCC27424 over the UCC27524.

  • 0 in reply to Richard Herring
    Prodigy 20 points
    Caution must be exercised when directly connecting OUTA and OUTB pins together because there is the
    possibility that any delay between the two channels during turnon or turnoff may result in shoot-through current
    conduction as shown in Figure 29. While the two channels are inherently very well matched (4-ns Max
    propagation delay), note that there may be differences in the input threshold voltage level between the two
    channels which causes the delay between the two outputs especially when slow dV/dt input signals are
    employed. TI recommends the following guidelines whenever the two driver channels are paralleled using direct
    connections between OUTA and OUTB along with INA and INB:
    • Use very fast dV/dt input signals (20 V/μs or greater) on INA and INB pins to minimize impact of differences
    in input thresholds causing delays between the channels.
    • INA and INB connections must be made as close to the device pins as possible.
    In this case, inA and inB are much faster then the limitation mentioned here. and since the delay matching is much better then in the ucc27424, 
    I do not understand your recommendation. 
    I will be glad to have someone from the team that developed this part with us in this issue.
    Regards Moshe