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UCC256302: About the system external stop function

Masazumi Ishii
Genius 3945 points
Part Number: UCC256302

Hello.

I have a question about UCC256302.

About the system external stop function

① About restoring from external system shutdown

⇒ When we confirmed the waveform, we started it after entering FAULT.

From the data sheet Figure 44, it does not apply to the condition to enter FAULT, and it does not understand the factor of entering FAULT.

 

② About operation in external stop

⇒ Data Sheet If you check with the operation in Figure 44, I think that it will shift to LIGHT_LOAD_RUN at the moment of short circuit and shift to 13 after 200 ms.

Assuming that the input voltage of LLC is sufficiently high and assuming BLKstart = 1, it shifts from JFET OFF to 3 → 4 and stays in WAKEUP (because it does not apply to the transition conditions of 4, 11, 15, 19).

Since it can shift to 11 when the voltage of Vcc becomes 10.7 V or less with the passage of time, it shifts to JFET ON.

Is it okay to recognize that you are repeating this situation?

(If the input voltage of LLC is low and BLKstart = 1 does not hold, I think I will stay at JFET OFF) b

 For details, please check the attached document.


Thank you.20180714_質問 (1).xlsx

  • 0
    TI__Mastermind 27095 points
    Hi Masazumi-san,

    Please allow me to clarify some things when FB is held low. When FB is held lower than the burst threshold for more than 200ms, it will transition to JFETOFF (state transition condition 13 in Table 3 of the UCC256302 datasheet). If the BLK pin voltage is greater than BLKStart, then the IC will move to Wakeup. It will stay in wakeup as long as the FB pin is held lower than the burst threshold. If VCC falls to 10.5V while FB is held low, the IC will re-enable the JFET to charge up VCC. Because no switching action is occuring, the VCC capacitance is not getting replenished from the bias winding and the VCC voltage will slowly decay. If FB is held low for an extended period of time, then you will see VCC periodically charge up and slowly drain. This behavior is expected.

    Regarding the fault, it is likely the controller hit OCP during the release. If I could suggest another option to disable the controller, try using the standby signal to pull BLK below BLKStop. This will force the controller to go through soft start when releasing the disable signal.

    Best Regards,
    Ben Lough