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TPS50601-SP: TPS50601 questions

Hoi Wa Ip
Intellectual 720 points
Part Number: TPS50601-SP

Hi Ti experts,

I have some questions regarding TPS50601-SP. Would you please kindly help to clarify? Thank very much.  

1. On TPS50601-SP data sheet page9 (electrical characteristics) - What’s the meaning of “minimum off time” and test condition? If minimum off time is 500ns, does it mean the duty cycle must be smaller than 50% at 1MHz (max on time = period –min off time = 1us-500ns=500ns)?

2. On TPS50601-SP data sheet Page13 (Typical characteristics)  - 

What’s the difference between minimum controllable on-time and duty ratio?
For example, as in fig15, the minimum controllable on-time at 25degree is 100ns, so the minimum controllable duty ratio should be (assume frequency is 500kHz): 100ns/2us = 5%. But in fig 16 it is higher than 5%.
Why there is this difference?

Best regards,

Peter

  • 0
    TI__Expert 7445 points
    Hi Peter,

    Minimum off-time information you need to determine minimum PVIN input voltage that would be necessary for the application as highlighted in equation #3 as well as indicated in Fig. 17. Thus depending upon the switching frequency one is operating at it will highlight what minimum input voltage (PVIN) that is necessary.

    If minimum off time is 500ns, does it mean the duty cycle must be smaller than 50% at 1MHz (max on time = period –min off time = 1us-500ns=500ns)?

    Yes you are correct in your assessment with regards to the Maximum duty cycle.

    Minimum controllable on-time implies that at start up when are going thru soft-start condition you will notice non-smooth turn-on at very low voltage less than 0.8V that is due to the fact when the duty cycle is very small one can not control it whether the converter is off or on.
    In other words if you go below the min controllable on-time one can not guarantee if the pulses will be off or on. Thus you must design to ensure that minimum duty cycle is greater than the min controllable on-time.

    I would need to look into fig. 15 and Fig 16 more closely and the test conditions and will get back to you on it.
  • 0 in reply to Ramesh Khanna
    Intellectual 720 points

    Hi Ramesh,

    Thank very much. I am looking forward to your reply soon. 

    Best regards,

    Peter