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SM72445: SM72445 in boost mode

Alinaghi Marzoughi
Prodigy 10 points
Part Number: SM72445
Other Parts Discussed in Thread: SM72442,

Tool/software:

SM72442 has a circuit in its demo board (SM3320) where there is a boost startup circuit for when battery voltage > panel voltage. 

SM72445 on the other hand, does not have such circuit in its datasheet or its application note. Given the info in table 2 of SM72445 datasheet where there is discussion on starting boost ratio of 1:1 or 1:1.2, do we still need the boost startup circuit if SM72445 used? 

Other question is, what are the min and max duty cycles possible with this chip?

  • 0
    TI__Guru 61695 points

    Hello Alinaghi,

    As far as I can see, your expectation seems to be correct, but I am not 100% sure. Do you have some SM72445 which you could use on the SM3320 for checking it out?

    For the other question: As this is not given in the datasheet, I cannot answer this question at the moment. I will try to find some information on it, but it might be difficult to get it. A test on the SM3320 might be the fastest way to get a typical value.

    Best  regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 10 points

    I ordered some SM72445 and put them on SM3320. The startup behavior was the same, and converter needed a boost kick signal, otherwise boost operation would not start. 

    Thanks for the suggestion on the second question. Will try some experiments to find out min and max duty cycle. 

  • 0 in reply to Alinaghi Marzoughi
    TI__Guru 61695 points

    Hello Alinaghi,

    Thank you very much for the feedback on the startup.

    When checking some measurements on the SM3320 board, I have seen on-times of the low-side switch in the range of 400ns. I do not know if this is the minimum on-time, but possibly this is a starting point for you.

    Best regards,
    Brigitte