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ISO5852S-Q1: How can we trigger the soft turn-off function of this chip?

Jerry Cong
Prodigy 50 points
Part Number: ISO5852S-Q1
Other Parts Discussed in Thread: UCC21750

Hello,

The problem we are facing is that we cannot see the soft turn-off from the output pin after the Desat protection is triggered. The output of the chip turns to VEE2 only within around 50 ns after the desat is triggered.

The following figure is the schematic we use for this chip. We suspect whether it is because we short OUTL and OUTH before the turn-on and turn-off resistor?  

 

Also, according to figures 15-18 of the datasheet of ISO5852SQDWRQ1, the soft turn-off waveform is generated with the existence of CL. But the datasheet doesn't specify where the CL locates in the application circuit. So I am wondering where we should place the CL and whether it is necessary for the soft turn-off of the gate drive chip?  

Thank you in advance for helping out and best regards,

Jerry

  • 0
    TI__Guru**** 189399 points

    Hi, Jerry,

    CL represents the load capacitance of the gate of the power switch being driven.

    Unfortunately, your attachments don't show up. Can you use the Rich Editor and attach them using the icons there?

  • 0 in reply to Don Dapkus
    Prodigy 50 points

    Hi Don,

    Thanks for your reply. Can you see the figure? L_gate will go to a current booster chip instead of the gate of the power device.

    We can trigger the short circuit protection and can see the change of FLT output in the primary side, but we cannot see the soft turn-off waveform as the figure 15 shown in its datasheet from L_AMC point. We suspect whether it is because we short OUTL and OUTH before the turn-on and turn-off resistor? 

    Best,

    Jerry

  • 0 in reply to Jerry Cong
    TI__Guru**** 189399 points

    Hi, Jerry,

    Thanks for reposting the picture! I can see it now.

    This gives some more details for using STO with a current buffer:

    Let me know if you have further questions.

  • 0 in reply to Don Dapkus
    Prodigy 50 points

    Hi Don,

    Actually, a MOSFET based gate drive chip is used as a current booster. Is there any way for us to realize the soft turn-off of the gate drive chip? We do have another functional block to serve as a real soft turn-off but we are wondering whether we can trigger the soft turn-off of the chip with the existing structure.

    Here, I attach a test result. We can see that the output pin (CH 1) goes down very quickly after the Desat detection.  

    CH 1: H_AMC CH 3: Desat Pin

    Thanks,

    Jerry

  • 0 in reply to Jerry Cong
    TI__Guru**** 189399 points

    Hi, Jerry,

    Have you seen our UCC21750? It can replace both ISO5852 and the IXYS driver. Should be a lot more straightforward.

    On the UCC21750 d/s, please read this section: 9.2.2.8 Higher Output Current Using an External Current Buffer