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UCC28631: IC Lockout and not restarting

Maitriya Damani
Prodigy 175 points
Part Number: UCC28631
Other Parts Discussed in Thread: UCC28630

Tool/software:

Hi Team, A customer of mine is facing the following problem with the low power startup .

I have been designing a Switching Supply based on the UCC28631 and we are looking at going into production early next year. Recently I have noticed a potential issue and am wondering if Texas Instruments has a solution.

Due to the low standby power requirements coming into effect next year the SNT has been designed with this in mind and has a <200mW standby at 230Vac and with the target application connected it is a little over 400mW.

In certain circumstances the IC will actually lock out and not restart. This occurs sometimes when the AC power is turned off briefly. To get the IC to restart you have to disconnect the AC input and wait for the bulk capacitor to drain completely which takes quite a while with the low standby power. 

Has this issue been noticed before and is there an easy solution?

Could you help with the same?

Best,

Maitriya

  • 0
    TI__Mastermind 24375 points

    Hi Maitriya,

    Thank you for reaching out.

    I think it might be better to check if any latching fault is occurring during this process causing the system to go into power on reset level and then restart again. Please check the sizing of  Vdd capacitor. Please put some bleeder resistor across bulk capacitor as well. Although this might increase power dissipation slightly, it might help here.

    Here are the list of fault codes from the SD pin count. The fault-code pulse train starts with a ~30-us positive pulse (start-pulse - can used for scope trigger), then a train of ~1-us positive pulses, then a low interval of ~10 us to signify end of the pulse train. Count the number of 1-us pulses in between the start/end. The following is fault code map for UCC2863x devices.

    4 - VDD overvoltage
    5 - VDD undervoltage
    12 - overlaod timer time-out - only for UCC28630
    14 - AC (i.e. bulk cap level) under-voltage detection while running
    15 - overtemperature internal (die temp)
    18 - SD pin fault
    20 - output overvoltage
    21 - VSENSE pin fault
    22 - DRV pin fault
    23 - CS pin fault
    24 - X-cap discharge event triggered - only for UCC28630/3
    25 - AC (i.e. bulk cap level) under-voltage detection before startup or restart
    26 - external overtemperature fault (SD pin pulled low

    Regards,

    Harish