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TPS56C215EVM-762: tps56C15 HICCUP protection and restart

Nini Zhong
Expert 7735 points
Part Number: TPS56C215EVM-762

Hi team ,

I have test the hiccup protection mode of TPS56C15. I have some confusion which might needs your help and support .

1. About over current protection

 As is shown in the datasheet ,"the UVP comparator detects it and shuts down the device after a wait time of 1 ms , the device restarts after a hiccup time of 7 ms .  " From my perspective , when over current happens , the vout is pulled down until to 0.68 vout_normal , after which the hiccup mode is triggered .Basically speaking , the over current protection finally triggers the under voltage protect , doesn't it ?

2 . Waiting time

I have read the Meng Liu's e2e question , though there are still some more confusion . Firstly , the waiting time is still 1ms according to my test (where current is 13A and Vout is drained down to 0.8V, first protection ). After a gap of 18ms , restart is triggered . And the voltage ramps up to 1V , which takes about 1 ms (not 4.7ms ?) I'm confused why not 4.7 ms ? Also thw waiting time when Iout stays at 13A and vout at 0.8V is longer than first protection . Is that because the converter is still on the soft start mode , in which case the device can tolerate longer under voltage period ? Can you give me some instruction and how the protect is implemented during soft start mode ?

3. Gap time

I have read Meng Liu 's question and the answer is that the gap time between two hiccup protection lasts about 7 cycles (of soft start time ) other than the 7 ms recommended in datasheet . However , according to my testing results , the gap time is 25 ms , which does not equal to 7 times 4.7 . I am a little confused . Can you give me some suggestions and guidance ?

4. The vout ripple

As I' m concerned , in FCCM mode the Vout ripple stays the same whatever the load current . However , the ripple varies ab little when I change the load current , which can been seen in the picture below.

The left I_load is 5A, the right is 10A

What's more, the DCM MODE . Base on the dcm theory , the vout ripple should be larger than that of ccm . However , according to my test , the conclusion is inverse . Can you give me some suggestions ?

Thanks a lot for your help and time !

  • 0
    TI__Mastermind 18510 points

    Our team will check and give some feedback today or tomorrow 

    yuchang

  • 0
    TI__Expert 4360 points

    Hi Nini,

    1.Yes, the over current protection finally triggers the under voltage protect.

    2.The result  is tested by EVM board as shown in the figure. CH1=SS, CH2=Vout, CH3=SW  CH4 = Iout, Iout from 12A to 15A

    No soft start (t1):  When the UVP was be triggered, the dalay time is 1 ms (t2), then the device shuts down.

    Soft start(t4): When the UVP was be triggered, the dalay time is one cycle(t4).

    The device restarts after a hiccup time of 7cycle(t3).

    3. Why the soft start time is not equal to 4.7ms (ss pin with 0.047uf capacitance)? The reason is that the softstart time of datasheet is typical value,  the real soft start time of EVM board have some deviation.

    4.The ripple waveform you captured should be not accuracy. I suggest to re-test it by referring to the EVM test guide, check the waveform with shortest probe ground to reduce the high-frequency noise coupling. and set proper horizontal scale.

    Xueliang