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UCC5870-Q1: Secondary Side ASC on Powerup

Andrew Bevelhymer
Prodigy 20 points
Part Number: UCC5870-Q1

Tool/software:

We are trying to make our gate drivers go to ASC mode on reset by holding AI5 and AI6 at approximately 3.4V. In order to not trigger other safeties which are enabled on reset, we tried the following:

1. Pulling AI2 and AI4 to GND2 to not trigger OCP/SCP

2. Pulling VCECLP to GND2 to keep the voltage at that pin below the threshold

Additionally, CLAMP is left floating since we are not using the Active Miller Clamp.

When the gate driver powers on, it does not drive the gate on.


Based on the ASC Implementation Flowchart (Figure 7-27 in datasheet,) we weren't sure whether or not this would only work with VCC1 down, so we removed VCC1 with the above configuration and witnessed the same behavior.

  • 0
    TI__Expert 5790 points

    Hi Andrew,

    Thanks for reaching out!

    I have a few questions:

    1. is VCC1 powered during this test?

    2. After the test, do you read any faults? (VCC2 should remain powered while connecting SPI to read faults)

    3. Is the test condition a clean power up, or did just VCC2 or just VCC1 lose power? If only one rail is power cycled, ther ewill be faults on the other side of the isolation barrier that will override ASC.

    4. What is the measured voltage at the AI5/6 pins during this condition?

    For our next gen SPI programmable gate driver, UCC5880, we have updated the priority of the ASC to work more consistently on power up.

  • 0 in reply to Daniel Norwood
    Prodigy 20 points

    1. We tried with both VCC1 powered up and with VCC1 powered down and noticed the same behavior

    2. We did not try reading any faults with SPI, but did see that nFLT1 was active (when VCC1 was powered up)

    3. The test was a clean power up. We tried:

    * VCC1 and VCC2 Powered Down -> Power up both VCC1 and VCC2 -> Measure output of gate driver

    * VCC1 and VCC2 Powered Down -> Power up only VCC2 -> Measure output of gate driver

    4. I did not write down the exact measurement unfortunately, but it was approximately 3.4V. We had to play with this quite a bit to get it to that point, since it seems there is some non-negligible impedance looking into AI5/AI6 at startup.

    For 2 and 4, if it will be useful I can try to repeat those tests and look at the faults/measure the exact voltage on the AI5/AI6 pins.

    That's good to hear on the UCC5880.

  • 0 in reply to Andrew Bevelhymer
    TI__Expert 5790 points

    Hi Andrew, Thanks for the quick feedback. Secondary ASC should work on a clean power up, as long as the power up fault conditions are avoided.

    Andrew Bevelhymer said:
    4. I did not write down the exact measurement unfortunately, but it was approximately 3.4V. We had to play with this quite a bit to get it to that point, since it seems there is some non-negligible impedance looking into AI5/AI6 at startup.

    As long as you paid attention to the increased current into these pins this shouldn't be the root cause. This current is from an internal diode to VREF, so if VREF is unpowered (As it is on power up if you use internal VREF) then the capacitors on VREF will be charged through AI5/6.

    Reading the faults is probably the easiest way to debug, some faults beyond what you listed that could be occurring are:

    Desat fault, if the DESAT pin is floating or a power module is not connected. This can be checked by seeing if the output starts to turn on at all.

    Regards,

    Daniel