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UCC21710: UCC21710 De-SAT protection

Sandeep J
Prodigy 10 points
Part Number: UCC21710

Tool/software:

In UCC21710, can I use the current source available in pin AIN for the design of De-SAT protection in a conventional way?

  • 0
    TI__Expert 6670 points

    Hi Sandeep, 

    I would not recommend using AIN for DESAT protection purposes. DESAT usually requires fast protection time - under 10us for IGBTs and 2-3us for SiC, and I'm not sure the bandwidth and the delay of the AIN channel can satisfy that requirement. 

    I recommend only using DESAT pin to monitor Vds/Vce voltage for DESAT purpose, and using AIN pin to monitor relatively constant signals - for example DC bus voltage and thermistor readings. 

    Thank you, 

    Vivian

  • 0 in reply to Vivian Qi
    Prodigy 10 points

    Thank you Vivian for your reply.

    I don't want AIN pin to monitor Vds/Vce. The monitoring and protective action will be done by OC pin only. Rather than making use of Vdd to monitor Vce/Vds, I thought if it is possible to use the current source available at AIN pin. This will be possible if I connect OC pin to AIN pin and use conventional DESAT protection circuit. Will it be okay to do so?

  • 0 in reply to Sandeep J
    TI__Expert 6670 points

    Hi Sandeep, 

    Do you want to increase the current into the DESAT decoupling capacitor by using AIN pin current source? 

    I would not recommend it because: 1. DESAT pin has an internal current source of 500uA already, so theoretically you do not need an additional current source if 500uA suits your need; 2. AIN pin has an operating min/max voltage of 0.6V to 4.5V. When DESAT is triggered, the DESAT voltage can rise to above 9V, which may damage the AIN pin. 

    Thus, if you want to increase DESAT blanking capacitor charging current, I would still recommend adding a charging path from VDD, or from OUTH. 

    Thanks, 

    Vivian

  • 0 in reply to Vivian Qi
    Prodigy 10 points

    Hi Vivian,

    In UCC21710, there is no DESAT pin, instead we use OC pin. OC pin doesn't have an internal current source. OC pin serve the purpose of DESAT protection by creating a current source from Vdd. Please see the figure below for your reference.

    Now, my doubt is, whether it is recommended to use the current source of AIN to drive the DESAT protection through OC pin. This could help me to avoid the resistor network that serves the purpose of making a virtual current source.

  • +1 in reply to Sandeep J
    TI__Expert 6670 points

    Hi Sandeep, 

    Understand, sorry for mistaking the question. 

    I think that is possible - I just ran a quick simulation. You should have a resistor divider network (R1/R2) to make sure OC pin voltage does not exceed 0.7V during normal operation, and make sure AIN pin never exceed 5V. So, if your Vds/Vce drop is too high, it's possible that this approach would not work. 

    We've never actually tested this and never seen other customers do this, so I can't speak on the recommendation part. 

    Hope this helps, 

    Vivian

  • 0 in reply to Vivian Qi
    Prodigy 10 points

    Dear Vivian,

    Thank you for the reply.

    I will get back if we do this successfully.