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UCC28950：Output short circuit protection and over current protection

user4657807
Prodigy 120 points
Part Number: UCC28950
Other Parts Discussed in Thread: UCC28951,

Can this IC provide DCDC output short-circuit protection and over-current protection? What is achieved by? Is it achieved by cycle-by-cycle current limit or peak-current mode control?

  • 0
    TI__Mastermind 25570 points

    Hello

    The UCC28950 and UCC28951 both provide over current and short circuit protection. Please have a look at the section of the Data Sheet dealing with this topic - I've included the most relevant information below.

    If the signal at the CS pin plus the added slope compensation ramp (see Fig 36 in the DS) reaches 2V the Cycle-by-Cycle ILIM comparator trips and terminates the switching cycle. As this overload condition persists then the SS/EN pin is discharged and switching stops once the SS/EN pin drops below the Hiccup threshold (typ 3.6V).

    Note that this mechanism is active in both Voltage Control Mode and in Peak Current Control mode.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Prodigy 120 points

    Alright, thank you very much. It's just not quite certain that short circuit protection can be achieved by primary limitation. In my understanding, secondary direct shutdown is reliable. Now I'm sure.

  • 0 in reply to user4657807
    TI__Mastermind 25570 points

    Hello

    Output SHORT CIRCUIT protection using the primary current works and is effective and uses the primary current sensing network which is needed in any case for peak current mode control (PCM) or for current limiting (Voltage Mode) so that there are no added circuit components.

    Hiccup modes reduce the average power dissipation while in short circuit but if you are using the primary current to control the output then the currents during the active part of the hiccup will be larger as Vin increases and smaller as Vin decreases. Normally Vin is from a PFC stage so Vin is relatively fixed so this behaviour is not a problem. If Vin varies over a wide range then it might be necessary to add a separate output current limiting circuit, but you will still need to sense the primary current for control purposes.

    Regards

    Colin