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Original question:

UCC21520: Strange behavior on the high side of UCC21520

UCC21520: ucc21520 abnormal output

Hangjie Wang
Intellectual 1270 points
Part Number: UCC21520


Hi expert,

In the SOP project, my customer found that UCC21520 has a case of abnormal output. Check that the low-voltage side is working normally. The high-voltage side customer has measured the auxiliary power supply current is normal(NO big current), VDD, VSS impedance is normal, but the output is always low, after ABA, the fault no longer exists, and now you need to provide the following help:
1. Potential reasons that may cause the output to have no waveform
2. The withstand voltage parameters of the internal diode


Any idea pls let me know, thanks.

  • 0
    TI__Mastermind 23226 points

    Hi Hangjie,

    1. If the output is always low, and an ABA swap fixed the issue, the driver could have been broken or not completely soldered down. How many units have this issue in production? Does the input side power supply also draw normal supply current? Sometimes customers have issues with missing pulses related to noise on the deadtime pin, but not a completely disabled output. How is the DISABLE pin connected? Can you share a screenshot of the schematic around the UCC21520?

    2. The output stage is composed of NMOSFETs, which in reverse appear as a diode. The reverse withstand voltage of that diode is therefore 30V, being the VDD-VSS abs max rating. The forward power rating is usually rated as a current, since the voltage is supposed to clamp around 0.7V. You could probably derive a safe continuous power level based on the power and the thermal coefficient of the part. Transient current would be more challenging to identify exactly. But If the OUT was shorted to VSS, there would be high supply current.

    Best regards,

    Sean