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Original question:

UCC5870-Q1: Clamp to gate diode

UCC5870-Q1: Actual max peak drive current

Shangjian Dai
Prodigy 30 points
Part Number: UCC5870-Q1

Hi,

I am wondering that can the max 15 A peak drive current be fully exploited? If not, what would be the suggested margin?

Regarding determining the max peak current needed, can the simple estimation i.e. (VCC-VEE)/Rg_min be used or it should be estimated with more accurate model or by experiment? 

Thanks.

Best Regards,

Shangjian

  • +1
    TI__Prodigy 255 points

    Hi Shangjian, 

    Thanks a lot for your questions. Below are my comments. 

    1) Yes, the max 15A peak drive current can be fully exploited. 

    2) The output current is limited by two factors.

    The first one is the saturation of output stage of the gate driver. We have not obtained the exact value of the output stage saturation current since our tests are always with external circuits, parasitic inductance, etc. But for UCC5870-Q1, this saturation current should be above 30A. The 15A maximum claimed in the datasheet is related with external circuit and is to leave certain margin. 

    The other one is (VCC-VEE)/Rg_min. In practical situations, you may also want to include the effect of parasitic inductance and the load capacitance to better estimate the peak current. 

    The peak current should be the smaller one of the saturation current and the current determined by external circuit, such as (VCC-VEE)/Rg_min in ideal case.  

    Hope this helps. Have a nice day. 

    Best regards, 

    Yongbin 

  • 0 in reply to Yongbin Chu
    Prodigy 30 points

    Hi Yongbin,

    Thanks very much for your answers. It helps a lot.

    Best Regards,

    Shangjian

  • 0
    Prodigy 100 points

    Hi Yongbin,

    We would like to use the UCC5870-Q1 with the FF900R12ME7_B11 IGBT module from Infineon. 

    This module is rated at 1200V 900A and has very low conduction losses but very high Gate Charge of 14.3uC for +/-15 gate drive.

    The device has an internal gate resistance of 0.5R and is recommended to be used with an external Rgate of 0.51R so total resistance 1R.

    We are likely to only use -10V  (or -12V) has the negative gate voltage (instead of -15V) but the still is going to put the peak gate current demand around 25A (25V/1R).

    Is this still okay for the UCC5870? Switching frequency would be 10kHz max.

    Figures 6-1 and 6-2 in the datasheet seem to indicate that 25A is okay but I don't know why TI don't increase the rated 15A drive current value if this is really safe?

    Is it possible the rated value will be increased in future or another part with higher rated current released?

    Please let me know if this is pushing the UCC5870 too hard.

    Best Regards

    Scott

  • 0 in reply to Scott Osborne
    TI__Prodigy 255 points

    Hi Scott, 

    Thanks very much for your follow up questions. UCC5870 is okay for your application and it can give 25A peak current. 

    The rated 15A in the datasheet is related with external circuit and is for extra margin. We do have a plan to update the UCC5870 datasheet to 30A drive current in the near future to avoid confusion. 

    Best regards, 

    Yongbin