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UCC256403: Howe to deal with HS

人在江湖
Intellectual 705 points
Part Number: UCC256403
Other Parts Discussed in Thread: UCC25640, UCC256404,

For the UCC25640* application customers put forward three points.

1) Since the customer input is high-voltage 800VDC, the customer intends to use the isolation driver for the upper tube driver. The customer does not know how to deal with the pin HS. Can the HS pin be grounded? What if it can't? For driver, it similar to Infineon's 1EDI20N12AF.

2) The UCC25640* enters the Burst Mode at approximately the number of load points. For example, under the same conditions, NCP1399 will enter burst mode when the load is less than 50%, while L6599 will enter burst mode when the load is less than 20-30%.How about UCC25640 *?

3) When the UCC25640* enters and exits the burst mode, it has burst soft-on and burst soft-off functions. Does this function change and influence the frequency? The L6599 used by the customer was difficult to handle when entering and exiting burst mode.

  • 0
    TI__Genius 9790 points

    Hi, James

    here is my answer to your question 

    1. HS of UCC25640X is need to connect to middle point of half bridge of LLC, because it need the HS signal to realize adaptive dead time control. Since the voltage rating of HS in 640V, it is not recommended to use UCC25640X in 800VDC application.

    2. the burst mode threshold of UCC25640X is programmable,  most of customers design burst mode threshold at around 10% of full load.

    3. There are several parts in family of UCC25640X, UCC256403 and UCC256404 has burst soft -on and burst soft-off function. The function is realized by changing switching frequency.

    Yunsheng

  • 0 in reply to Yunsheng Qu
    Intellectual 705 points

    About 10% burst mode should be for constant voltage output applications, but will it be so low for LED applications with constant current? For example, when the light is lowered to about 5V under 80% load, the output voltage may only be about 60% of the full load voltage. This application will enter the burst mode earlier than the constant voltage application.

  • 0 in reply to 人在江湖
    TI__Genius 9790 points

    you are correct, 10% burst mode design is for constant voltage output application.

    But the minimum burst mode threshold of UCC25640X is only 0.2V, the full range of VCOMP is 6V. if the K=Lm/Lr is around 8~10, it can keep UCC25640X out of burst at  10% dimming.

    Yunsheng