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Original question:

UCC21710-Q1: UCC21710-Q1:

UCC21710-Q1: How to connect OC for desaturation and CLMPI for active miller clamp when BJT current buffer is used

CharliePE
Intellectual 255 points
Part Number: UCC21710-Q1

Hi,

When the BJT current buffer (shown on page 46 of the datasheet of UCC21710-Q1 and the E2E post e2e.ti.com/.../798930 is used to increase the driving current capacity, how should the two pins OC and CLMPI be connected to accomplish desaturation and active miller clamp?

Should we still use the circuit shown on page 41 of the datasheet to connect pin OC for desaturation, and directly link the gate of the MOSFET (the actual switching component being driven by the BJT current buffer) to CLMPI pin for active miller clamp?

Also the post for soft-turn-off circuit in the E2E post shown above is no longer available. Can you show details of how to design the soft-turn-off with a resistor and capacitor between the base of the transistor and VEE?

Thanks.

  • 0
    TI__Expert 4875 points

    Hello,

    Yes, both functions are implemented with the same connection as given in the datasheet. The buffer only presents some difference in the STO circuitry because the buffer is driven with OUTL (instead of OUTL directly connected to the MOSFET gate), thus OUTL cannot control the STO current successfully unless there are some added components. The Miller clamp pin, CLMPI, must still be directly connected to the gate of the MOSFET in order to provide a low-impedance path to VEE in order to prevent false turn-on. The DESAT circuit with OC pin is also same as shown in the datasheet. 

    Please see the datasheet section entitled "Higher Output Current Using an External Current Buffer" for choosing the R and C value for controlling STO when using an external BJT buffer. Additionally, see the XL Calculator tool here that also has a sheet for calculating the R/C values for STO with Buffer and the resistors for DESAT circuit using the OC protection.

    Regards,

    Audrey

    Please click the green button if I answered your questions! 

  • 0 in reply to Audrey Dearien7
    Intellectual 255 points

    Hi Audrey,

    Thank you very much for providing insightful, accurate, and prompt reply. Your help is highly appreciated.

    Have a great day,

    Guanghui