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TPS54062: What will happened when TPS54062 is over load?

Leo Yang
Expert 5595 points
Part Number: TPS54062

Hi team

What will happened when it is over load? My customer's application is Vin 35V and Vout 5V. And they are wondering what happened when Iout is over 0.05A.

I see frequency foldback in this situation. If so, could you give more explain in why frequency foldback can help in over load. Thank you.

BR

Leo

  • +1
    TI__Mastermind 30955 points

    Hi Leo,

    In frequency foldback, the switching frequency is decreased. Basically when output is overloaded, the duty cycles required can be quite small, since output voltage is low. This also means that the slope of the falling inductor current is also quite small, since it is proportional to Vout/L. In order to prevent the part from violating the minimum on-time, the part decreases the switching frequency, allowing the part to still switch at the required duty cycle and to be above minimum on-time. If the required time that the switch is on goes below minimum on-time, the controller will have to keep the switch on for the minimum on-time instead, which overall will lead to current runaway.

    Regards,

    Richard 

  • 0 in reply to Richard Fu22
    TI__Expert 5595 points

    Hi Richard,

    Thanks for reply. BTW, how does TPS54062 detect the over load event? In the block diagram, it senses the high side switch peak current to compare with COMP voltage. on the other hand, datasheet mentioned 134mA typical value for current limit. In my application, is it still 50mA Iout limitation when Vin is 35V?

    BR

    Leo

  • 0 in reply to Leo Yang
    TI__Mastermind 30955 points

    Hi Leo,

    You're right, the high-side peak current is compared to the COMP voltage. The current limit is implemented by clamping the COMP pin to a maximum value. Basically, it is 134mA at 12Vin as shown in figure 17, but the table shows that it can be lower. Keep in mind that a small inductor size can mean high peak-peak ripple, which could be a reason for the part to enter current limit. 

    Regards,

    Richard