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UCC21520: lower MOS to lag behind the upper MOS by 60us

yong luo
Prodigy 210 points
Part Number: UCC21520
Other Parts Discussed in Thread: UCC21550,

Tool/software:

Chip bootstrap power supply, UVLO=8V.
Input 50kHz complementary PWM, and the chip output is shown in the figure below.

Green represents the upper MOS transistor, blue represents the lower MOS transistor, and yellow represents the bootstrap capacitor voltage.
Is it normal for the waveform emitted by the lower MOS to lag behind the upper MOS by 60us? If there are abnormalities, which directions?

  • 0
    TI__Genius 17076 points

    Hi Yong,

    Please use the UCC21550 instead. It is a much improved update to the UCC21520 IC design.

    Is CH2:Blue the gate driver that is powered by the bootstrap capacitor? 60us is close to the power-up delay of this gate driver. Therefore, bootstrap supply must be charged about around 50us before the output channel will turn on. 

    Best regards,

    Sean

    Datasheet reference clipping: