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Original question:

UCC21222-Q1: UCC21222-Q1: Testing issues

UCC21222-Q1: UCC21222-Q1: Testing issues

Mohana Krishnan M
Prodigy 215 points
Part Number: UCC21222-Q1

Hi,

The delay of diable pin is given to be 36ns to 50ns.

once the voltage on DIS reaches its threshold (or) 50%, it will take 36ns to 50ns for output to reach 90% of its threshold - refer figure 29 of datasheet.

But in actual case, i am able to see that as soon as it reaches threshold of ~2V, the output drops.

it is faster than that mentioned in datasheet. could there be any reason?

  • 0
    TI__Genius 10652 points

    Hi Mohana, 

    The typical delays may vary slightly if your test setup varies from the conditions specified for the characteristic in the datasheet, but should come very close to what is specced even in this case. One reason you are seeing a difference can be that the VIH to begin measurement of response time for DIS pin rising is typically 1.8V as in Section 6.9, and not 2V. Therefore response time may be measured from 1.8V of Disable pin rising edge to 90% of your Output peak. Could you let us know if this accounts for difference in response time? Please let us know more about your setup and whether the 

    Best,

    Dimitri

  • 0 in reply to dimitri james
    Prodigy 215 points

    Hi Dimitri,

    Thanks for your response.

    With 1.8V, the disable time is very large (in micro seconds).

    We have mosfet connected to the the gate driver as well.

  • 0 in reply to Mohana Krishnan M
    TI__Genius 10652 points

    Mohana,

    The typical delays as specified in the datasheet are measured with 0 load Capacitance, please try without load.

    Best

    Dimitri James

  • 0 in reply to dimitri james
    TI__Genius 10652 points

    Mohana, 

    Also, it was noted by a colleague that the rise time for your signal labeled EMER_STOP slews very very slowly (which i somehow didn't notice earlier, thanks to him for pointing it out), and this is likely the cause of the discrepancy you're observing in the DISABLE response time. With such a low rise time, the long time to dwell close to the VIH point can cause a slow switching situation; you want to "deliberately" pass through the VIH threshold an order of magnitude or less than the timescale youre looking to measure.

    Suggested to increase the slew rate of EMER STOP so that it is <0.1*Response time of disable listed. In other words, can you try to increase the rise time <3.6ns for your measurement?

    Best

    Dimitri